Electroconductive member, process cartridge, and image forming apparatus

ABSTRACT

Provided is an electrophotographic electroconductive member including an electroconductive support and an electroconductive layer on the support, an electroconductive member is used, in which an electroconductive layer has a matrix comprising a first rubber, and domains dispersed in the matrix, the domains each comprising a second rubber and an electronic electroconductive agent, and for impedance measured by applying an AC voltage with an amplitude of 1 V to the electroconductive layer while varying frequencies between 1.0×10 −2  Hz to 1.0×10 7  Hz under a specific environment, when a double logarithmic plot with a frequency on an abscissa and an impedance on an ordinate is obtained, a slope on a high frequency side is −0.8 or more and −0.3 or less, and the impedance a low frequency side is from 1.0×10 3  to 1.0×10 7 Ω.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Patent ApplicationNo. PCT/JP2019/016300, filed Apr. 16, 2019, which claims the benefit ofJapanese Patent Application No. 2018-079952, filed Apr. 18, 2018,Japanese Patent Application No. 2019-032936, filed Feb. 26, 2019, andJapanese Patent Application No. 2019-069097, filed Mar. 29, 2019, all ofwhich are hereby incorporated by reference herein in their entirety.

BACKGROUND

The present disclosure relates to an electrophotographicelectroconductive member that can be used as a charging member, adeveloping member, or a transfer member in an electrophotographic imageforming apparatus, a process cartridge, and the electrophotographicimage forming apparatus.

DESCRIPTION OF THE RELATED ART

An electroconductive member such as a charging member, a transfermember, or a developing member has been used in an electrophotographicimage forming apparatus. As the electroconductive member, anelectroconductive member having an electroconductive support and anelectroconductive layer on the support has been known.

The electroconductive member plays a role of transporting an electriccharge from the electroconductive support to a surface of theelectroconductive member and giving the electric charge to a contactobject by discharging or triboelectric charging.

The charging member is a member that causes discharge between thecharging member and an electrophotographic photoreceptor to charge asurface of the electrophotographic photoreceptor. The developing memberis a member that controls the electric charge of a developer applied onthe surface by triboelectric charging to give a uniform charge amountdistribution, and then, uniformly transfers the developer to the surfaceof the electrophotographic photoreceptor according to the appliedelectric field. The transfer member is a member that transfers thedeveloper from the electrophotographic photoreceptor to a print mediumor an intermediate transfer member, and at the same time, generates thedischarge to stabilize the transferred developer.

Each of these electroconductive members needs to achieve uniformcharging with respect to a contact object such as an electrophotographicphotoreceptor, an intermediate transfer member, or a printing medium.

Japanese Patent Application Laid-Open No. 2002-3651 discloses a rubbercomposition having a sea-island structure containing a polymercontinuous phase formed of an ionic electroconductive rubber materialmainly composed of a raw material rubber A having a volume resistivityof 1×10¹² Ω·cm or less, and a polymer particle phase formed of anelectroconductive rubber material made electroconductive by blendingelectroconductive particles in a raw material rubber B, and a chargingmember having an elastic layer formed from the rubber composition.

According to the study by the present inventors, it was found that thecharging member according to Japanese Patent Application Laid-Open No.2002-3651 is excellent in uniform charging property with respect to abody to be charged. However, it has been recognized that there is stillroom for improvement in speeding up an image forming process in recentyears. Specifically, when the charging member according to JapanesePatent Application Laid-Open No. 2002-3651 is subjected to the formationof an electrophotographic image, it is not possible to sufficientlylevel the minute potential unevenness formed on the surface of the bodyto be charged up to the charging step, and an electrophotographic image(hereinafter, also referred to as “ghost image”) in which an image thatis not supposed to be originally formed due to the potential unevennessis superimposed on the original image may be formed in some cases.

SUMMARY

One aspect of the present disclosure is directed to providing anelectroconductive member that can be used as a charging member, adeveloping member, or a transfer member that can stably charge a body tobe charged even when applied to a high-speed electrophotographic imageforming process.

In addition, another aspect of the present disclosure is directed toproviding a process cartridge that contributes to the formation of ahigh-quality electrophotographic image. Still another aspect of thepresent disclosure is directed to providing an electrophotographic imageforming apparatus capable of forming a high-quality electrophotographicimage.

According to one aspect of the present disclosure, there is provided anelectrophotographic electroconductive member comprising: a supporthaving an electroconductive outer surface; and an electroconductivelayer on the electroconductive outer surface of the support, theelectroconductive layer having a matrix comprising a first rubber, anddomains dispersed in the matrix, the domains each comprising a secondrubber and an electronic electroconductive agent, wherein assuming thata metal film is provided on an outer surface of the electroconductivemember, and impedance is measured by applying an AC voltage with anamplitude of 1 V between the electroconductive outer surface of thesupport and the metal film while varying a frequency between 1.0×10⁻² Hzto 1.0×10⁷ Hz under an environment of a temperature of 23° C. and ahumidity of 50% RH, and a double logarithmic plot with a frequency on anabscissa and an impedance on an ordinate is obtained, a slope atfrequencies of 1.0×10⁵ Hz to 1.0×10⁶ Hz is −0.8 or more and −0.3 orless, and the impedance at frequencies 1.0×10⁻² Hz to 1.0×10¹ Hz is1.0×10³ to 1.0×10⁷Ω.

According to another aspect of the present disclosure, there is provideda process cartridge configured to be detachably attachable to a mainbody of an electrophotographic image forming apparatus, the processcartridge for electrophotography including the electroconductive member.According to still another aspect of the present disclosure, there isprovided an electrophotographic image forming apparatus including theelectroconductive member.

Further features of the present disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an image view of surface potential unevenness.

FIG. 1B is an image view of the surface potential unevenness.

FIG. 1C is an image view of the surface potential unevenness.

FIG. 1D is an image view of the surface potential unevenness.

FIG. 2A is an image view of discharge omission.

FIG. 2B is an image view of the discharge omission.

FIG. 3 is an explanatory diagram of a graph of impedancecharacteristics.

FIG. 4 is an explanatory diagram of impedance behavior.

FIG. 5 is a sectional view perpendicular to a longitudinal direction ofa charging roller.

FIG. 6 is a schematic view of a sea-island structure.

FIG. 7 is an explanatory diagram of an envelope perimeter.

FIG. 8A is an explanatory diagram of a cross-section cutting direction.

FIG. 8B is an explanatory diagram of a cross-section cutting direction.

FIG. 9 is a schematic diagram of a process cartridge.

FIG. 10 is a schematic diagram of an electrophotographic apparatus.

FIG. 11 is a schematic diagram of a state where a measurement electrodeis formed on a charging roller.

FIG. 12 is a sectional view of a measurement electrode.

FIG. 13 is a schematic diagram of an impedance measurement system.

FIG. 14 is a schematic diagram of an image for evaluating a ghost image.

FIG. 15 is a diagram illustrating a logarithmic log plot obtained inExample 22.

FIG. 16 is an explanatory diagram of a method for manufacturing anelectroconductive member.

DESCRIPTION OF THE EMBODIMENTS

The present inventors presume that a charging member according toJapanese Patent Application Laid-Open No. 2002-3651 causes a ghost imageas follows.

A phenomenon in which a ghost image occurs will be described withreference to FIGS. 1A, 1B, 1C and 1D. In FIG. 1A, 11 represents acharging member, 12 represents a photosensitive drum, 13 represents asurface potential measuring unit before a charging process, and 14represents a surface potential measuring unit after the chargingprocess. Generally, the surface potential of the photosensitive drumthat has undergone the transfer process has unevenness as illustrated inFIG. 1B. Therefore, the unevenness of the surface potential rushes intothe charging process, and the charging potential unevenness asillustrated in FIG. 1C is formed according to the surface potentialunevenness, thereby generating a ghost image. Here, as long as thecharging member has a sufficient electric charge imparting ability toeven out the surface potential unevenness, the ghost image does notoccur.

However, it is considered that the charging member according to JapanesePatent Application Laid-Open No. 2002-3651 cannot sufficiently cope withthe shortening of discharge interval for a body to be charged due to thespeeding up of an electrophotographic image forming process. Themechanism is considered as follows.

Generally, in minute gaps in the vicinity of a contact portion betweenthe charging member and the photosensitive drum, discharge occurs in aregion where the relationship between the strength of an electric fieldand the distance between the minute gaps satisfies Paschen's law. In anelectrophotographic process in which a photosensitive drum rotates anddischarge is generated, it has been found that when one point on thesurface of the charging member is traced over time, the discharge doesnot occur continuously from a discharge start point to a discharge endpoint, and multiple discharges occur repeatedly. The present inventorshave measured and analyzed a discharge state of the charging memberaccording to Japanese Patent Application Laid-Open No. 2002-3651 indetail in a high-speed process using an oscilloscope. In the chargingmember according to Japanese Patent Application Laid-Open No. 2002-3651,the timing at which high-frequency discharge is unlikely to occur in acharging process portion, that is, a phenomenon in which dischargeomission occurs has been obtained. It is presumed that this is a resultthat the total discharge amount decreases due to the occurrence ofdischarge omission, and the unevenness of the surface potential cannotbe offset.

FIG. 2A and FIG. 2B are image diagrams of a state in which dischargeomission occurs. FIG. 2A illustrates a state in which there is nodischarge omission and the total amount of discharge is satisfied, andFIG. 2B illustrates a state in which the discharge omission occurs andthe total amount of discharge is insufficient.

It is presumed that the reason for the occurrence of the dischargeomission is that on the surface of the charging member, the supply ofelectric charge for the subsequent discharge cannot follow after thedischarge has occurred and the electric charge is consumed.

Therefore, on the surface of the charging member, in order to quicklysupply the next electric charge after the discharge has occurred and theelectric charge is consumed, the discharge frequency may be improved tosuppress the discharge omission.

Here, the present inventors consider that it is not sufficient to speedup the cycle of charging the electric charge inside the charging member.In other words, on the surface of the electroconductive member, thedischarge omission can be suppressed by speeding up the cycle ofelectric charge consumption due to the discharge and electric chargesupply. However, in a case where the amount of electric charge that cancontribute to this cycle is reduced by the amount of time required forthe cycle being shortened, a single discharge amount is reduced, and thetotal amount of discharge does not reach a level that evens out thesurface potential unevenness. Therefore, it was considered necessary notonly to suppress the discharge omission, that is, to improve thefrequency of the discharge, but at the same time to improve thegeneration amount of a single discharge.

Therefore, the present inventors have made extensive studies to obtainan electroconductive member capable of accumulating sufficient electriccharges in a short time and promptly releasing the electric charges. Asa result, it has been found that the electroconductive member having thefollowing configuration can meet the above requirements well.

The electroconductive member includes a support having anelectroconductive outer surface and an electroconductive layer on theelectroconductive outer surface of the support, the electroconductivelayer includes a matrix comprising a first rubber, and domains dispersedwithin the matrix, and the domains include a second rubber and anelectronic electroconductive agent. Assuming that a metal film isprovided on an outer surface of the electroconductive member, andimpedance is measured by applying an AC voltage with an amplitude of 1 Vbetween the electroconductive outer surface of the support and the metalfilm while varying a frequency between 1.0×10⁻² Hz to 1.0×10⁷ Hz underan environment of a temperature of 23° C. and a humidity of 50% RH, anda double logarithmic plot with a frequency on an abscissa and animpedance on an ordinate is obtained, both the following firstrequirement and second requirement are satisfied.

<First Requirement>

The slope at frequencies from 1.0×10⁵ Hz to 1.0×10⁶ Hz is −0.8 or moreand −0.3 or less.

<Second Requirement>

The impedance at frequencies from 1.0×10⁻² Hz to 1.0×10¹ Hz is from1.0×10³ to 1.0×10⁷Ω.

With the electroconductive member according to this aspect, it ispossible to form a uniform charging potential profile as illustrated inFIG. 1D without using a pre-exposure device for evening out the surfacepotential unevenness.

Hereinafter, the electroconductive member according to this aspect willbe described with reference to an aspect for a charging member as anexample. The electroconductive member according to this aspect is notlimited to the use as a charging member, and may be applied to, forexample, a developing member or a transfer member.

The electroconductive member according to this aspect includes a supporthaving an electroconductive outer surface, and an electroconductivelayer on the electroconductive outer surface of the support. Theelectroconductive layer has electroconductivity. Here, theelectroconductivity is defined as a volume resistivity of less than1.0×10⁸ Ω·cm. In addition, the electroconductive layer includes a matrixcontaining a first rubber, and domains dispersed within the matrix, andthe domains include a second rubber and an electronic electroconductiveagent. Further, the electroconductive member satisfies the above <firstrequirement> and <second requirement>.

<First Requirement>

The first requirement regulates that stagnation of electric charges inthe electroconductive member hardly occurs on the high frequency side.

When the impedance of the electroconductive member in the related art ismeasured, the slope is always −1 on the high frequency side. Here, theslope means a slope with respect to a horizontal axis when the impedancecharacteristics of the electroconductive member are plotted in alogarithmic log with respect to frequency as illustrated in FIG. 3.

The equivalent circuit of the electroconductive member is represented bya parallel circuit of electric resistance R and capacitance C, and theabsolute value of impedance |Z| can be expressed by the followingEquation (1). At this time, f in Equation (1) represents the frequency.

$\begin{matrix}{{Z} = \sqrt{\frac{1}{R^{- 2} + {\left( {2\pi \; f} \right)^{2}C^{2}}}}} & (1)\end{matrix}$

On the high frequency side, a straight line with an impedance slope of−1 can be presumed to be in a state where the movement of the electriccharge cannot follow the high frequency voltage and stagnates, and thuselectrical resistivity R greatly increases, so to speak, the insulationcapacitance is measured. It can be presumed that the state in which theelectric charge stagnates is a state in which R is approximated toinfinity in Equation (1). At this time, in Equation (2) in which adenominator element is removed, R-² can be approximated to a very smallvalue with respect to (2πf)²C². Therefore, Equation (1) can be modifiedby approximation with Equation (3) with R-² removed. Finally, ifEquation (3) is modified by taking the logarithm of both sides, itbecomes Equation (4), and the slope of log f becomes −1.

$\begin{matrix}{R^{- 2} + {\left( {2\pi \; f} \right)^{2}C^{2}}} & (2) \\{{Z} = \sqrt{\frac{1}{\left( {2\pi \; f} \right)^{2}C^{2}}}} & (3) \\{{\log \mspace{14mu} {Z}} = {{{- \log}\mspace{14mu} f} - {\log \left( {2\pi \; C} \right)}}} & (4)\end{matrix}$

The meanings of the above Equations (1) to (4) will be described withreference to FIG. 4. In FIG. 4, a vertical axis represents the logarithmof the absolute value of impedance, and a horizontal axis represents thelogarithm of the frequency of a measured oscillating voltage. FIG. 4illustrates impedance behavior expressed by Equation (1). First, asdescribed above, the absolute value of the impedance satisfying Equation(1) decreases at a certain frequency as the frequency increases.

In the logarithmic log plot as illustrated in FIG. 4, the decreasingbehavior is that the slope does not depend on the electrical resistivityor capacitance of the charging member, and the impedance draws astraight line having a slope of −1, as indicated in Equation (4).

When the impedance characteristics of an insulating electroconductivemember are measured, from the fact that the impedance draws a straightline having a slope of −1, the characteristics are presumed to appearthat when the slope is −1 in the measuring of the impedance of theelectroconductive member, the movement of the electric charge isstagnant on the high frequency side. When the movement of the electriccharge on the high frequency side is stagnant, the supply of theelectric charge for the discharge cannot follow the frequency of thedischarge. As a result, it is presumed that there is a timing at whichdischarge is not possible and thereby the discharge omission occurs.

On the other hand, in the electroconductive member having the impedanceslope of −0.8 or more and −0.3 or less in a high frequency region offrom 1.0×10⁵ Hz to 1.0×10⁶ Hz, the electric charge supply is unlikely tostagnate on the high frequency side. As a result, it is possible tosupply the electric charge to discharges of frequencies of from a lowfrequency range to a high frequency range where the impedance has aconstant value, particularly to discharges on the high frequency sidewhere the electric charge stagnation is likely to occur. Since theelectric charge can be sufficiently supplied, it is possible to suppressthe discharge omission and increase the total amount of the discharge.The range of the high frequency region is considered to be a regionwhere due to the discharge in a region at the highest frequency amongthe frequencies of the discharge generated from the electroconductivemember, the discharge omission is likely to occur. By indicating a valuein the above range in which the slope is larger than −1 in such afrequency region, the slope larger than −1 is obtained even in a highfrequency region lower than the frequency region, and the occurrence ofdischarge omission is suppressed so that the total amount of dischargecan be improved.

The present inventors consider that when the frequency of discharge isspecifically predicted by using a case where a charging roller forelectrophotography as a charging member and a photosensitive drum arecombined, the range is as follows.

The discharge region in a moving direction of the surface of thecharging roller, which is provided so as to face the outer surface ofthe photosensitive drum and rotates and moves in synchronization withthe photosensitive drum, is set to from 0.5 mm to 1 mm. If the processspeed of the electrophotographic apparatus is from 100 to 500 mm/sec atthe maximum, the time for the surface of the photosensitive drum to passthrough the discharge region is from 10⁻³ sec to 10⁻² sec or more. Inaddition, when observing the discharge in detail, the length of thedischarge region due to a single discharge is from 0.01 mm to 0.1 mm.Therefore, it is presumed that at least 5 to 100 times of discharges aregenerated while the same point on the surface of the charging rollerpasses through the discharge region. Therefore, it is presumed that thefrequency of the discharge generated by the charging roller is in therange of several Hz to 1.0×10⁶ Hz. As the process becomes faster, sinceit is necessary to increase the frequency of discharge to increase thenumber of discharges, the control of discharge and a conductionmechanism particularly in a high frequency region, among the aboverange, such as 1.0×10⁵ Hz to 1.0×10⁶ Hz is important.

As described above, in order to increase the number of discharges, it iseffective to make the impedance slope in the high frequency regiondeviate from −1. As a result, it is possible to achieve well thecharacteristic of rapidly supplying the electric charge for thedischarge and the subsequent discharge. When the slope of the impedancedeviates from −1, it means that the supply of the electric charges inthe electroconductive member is not stagnant, and thus the chargingmember can obtain the characteristic in the direction of suppressing thedischarge omission.

<Second Requirement>

The impedance on the low frequency side according to the secondrequirement represents the characteristic that stagnation of theelectric charges is unlikely to occur.

This can be seen from the region where the slope of the impedance on thelow frequency side is not −1. Then, in Equation (1), if the frequency isapproximated to zero, it can be approximated to the electricalresistivity R, and thus it can be seen that the electrical resistivity Rrepresents the ability of the electric charge to move in a singledirection.

Therefore, in the measurement while applying the low-frequency voltage,it can be assumed that the movement amount of the electric charges inthe state where the movement of the electric charges can follow thevibration of the voltage is simulated.

The movement amount of the electric charges at a low frequency is anindex of the ease of electric charge movement between the chargingmember and the measurement electrode, and it can an index of the amountof the electric charges that can be moved by discharge from the surfaceof the charging member to the photosensitive drum.

The amplitude of an AC voltage used for measuring the impedanceaccording to the first requirement and the second requirement is 1 V.This oscillating voltage for measurement is significantly lower than thevoltage applied to the charging member in the electrophotographic imageforming apparatus of several hundred V to several thousand V. Therefore,it is considered that the easiness of discharge from the surface of thecharging member can be evaluated in a higher dimension by measuring theimpedance according to the first requirement and the second requirement.

Further, by satisfying the second requirement, the easiness of dischargecan be controlled within an appropriate range. When the impedance islower than 1.0×10³ Ω, the amount of one discharge becomes too large, thesupply of the electric charges for the subsequent discharge cannot befollowed, and it works in the direction in which discharge is lost,which makes it difficult to suppress ghost images. On the other hand,when the impedance exceeds 1.0×10⁷Ω, the easiness of discharge isreduced, and the discharge amount is not enough to fill the surfacepotential unevenness.

In the charging member as described in FIG. 4, the absolute value of theimpedance takes a constant value in the low frequency region, and theimpedance at 1.0×10⁻² Hz to 1.0×10¹ Hz can be substituted with the valueof the impedance at the frequency of 1 Hz, for example.

The electroconductive member that satisfies both the first requirementand the second requirement can eliminate the unevenness of the surfacepotential of the photosensitive drum in the discharge amount in thefrequency range from the low frequency side to the high frequency sideto achieve the discharge at a level that suppresses ghost images. Bysatisfying the first requirement, it is possible to suppress thedischarge omission on the high frequency side. Further, by satisfyingthe second requirement, the dischargeability is further improved, andthe generation of the ghost image can be effectively suppressed.

<Method for Measuring Impedance>

The impedance can be measured by the following method.

When measuring the impedance, in order to eliminate the effect ofcontact resistance between the electroconductive member and themeasurement electrode, a low-resistance thin film is deposited on thesurface of the electroconductive member, and the thin film is used as anelectrode while Impedance is measured at two terminals using anelectroconductive support as a ground electrode.

Examples of the method for forming the thin film include a method forforming a metal film such as metal vapor deposition, sputtering,application of a metal paste, and attachment of a metal tape. Amongthese, the method for forming a metal thin film such as platinum orpalladium as an electrode by vapor deposition is preferable from theviewpoint of reducing the contact resistance with the electroconductivemember.

In a case of forming a metal thin film on the surface of theelectroconductive member, when considering the simplicity and uniformityof the thin film, it is preferable to use a vacuum vapor depositiondevice that applies a mechanism that can hold the charging member to thevacuum vapor deposition device, and further applies a rotation mechanismto an electroconductive member having a cylindrical cross section. Forthe cylindrical electroconductive member whose cross section is formedof a curved surface such as a circular shape, it is difficult to connectthe metal thin film as the above measurement electrode and the impedancemeasuring device, and thus the following method is preferably used.Specifically, the measurement may be performed by forming a metal thinfilm electrode with a width of from 10 mm to 20 mm in the longitudinaldirection of the electroconductive member, then winding the metal sheetwithout gaps, and connecting the metal sheet with the measurementelectrode coming out of the measuring device. With this, the electricsignal from the electroconductive layer of the electroconductive membercan be suitably obtained by the measuring device, and the impedancemeasurement can be performed. The metal sheet may be any metal sheethaving an electrical resistivity equivalent to that of the metal portionof the connection cable of the measuring device when measuring theimpedance, and for example, an aluminum foil or a metal tape can beused.

The impedance measuring device may be an impedance analyzer, a networkanalyzer, a spectrum analyzer, or any other device capable of measuringimpedance in the frequency region up to 1.0×10⁷ Hz. Among these, it ispreferable to measure with an impedance analyzer from the electricresistance range of the electroconductive member.

The impedance measurement conditions will be described. The impedance atthe frequency region of from 1.0×10⁻² Hz to 1.0×10⁷ Hz is measured byusing an impedance measuring device. The measurement is performed in anenvironment of temperature of 23° C. and humidity of 50% RH. In order toreduce the measurement variation, it is preferable to provide five ormore measurement points per digit of frequency. The amplitude of the ACvoltage is 1 V.

Regarding the measurement voltage, the measurement may be performedwhile applying the DC voltage in consideration of the shared voltageapplied to the electroconductive member in the electrophotographicapparatus. Specifically, it is suitable for quantifying thecharacteristics of transport and accumulation of electric charges bymeasurement while applying the DC voltage of 10 V or less on anoscillation voltage.

Next, a method for calculating the impedance slope will be described.

For the measurement results measured under the above conditions, using aspreadsheet software (for example, “Windows Excel” (product name,available from Microsoft), the absolute value of the impedance isplotted in a logarithmic log graph against the measured frequency. Theslope of the absolute value of the impedance in the frequency region of1.0×10⁵ to 1.0×10⁶ Hz in the graph obtained by this logarithmic log plotmay be obtained by using the measurement points in the frequency regionof 1.0×10⁵ to 1.0×10⁶ Hz. Specifically, for the plot of the graph in thefrequency range, an approximate straight line of the linear function maybe calculated by a least squares method, and the slope thereof may becalculated.

Then, an arithmetic average value of the measurement points in thefrequency region of 1.0×10⁻² to 1.0×10¹ Hz in the logarithmic log graphis calculated, and the obtained value may be used as the impedance onthe low frequency side.

When measuring the slope of the impedance of the cylindrical chargingmember, the measurement is performed at five points at any location ineach region when the longitudinal direction as the axial direction isdivided into five parts, and the arithmetic average value of themeasurement value of the slope at five points may be calculated.

The electroconductive member according to this aspect will be describedwith reference to FIG. 5 by taking an electroconductive member having aroller shape (hereinafter, an electroconductive roller) as an example.FIG. 5 is a sectional view perpendicular to a longitudinal direction,which is an axial direction of the electroconductive roller. Theelectroconductive roller 51 has a cylindrical electroconductive support52, and an electroconductive layer 53 formed on the outer periphery ofthe support 52, that is, on the outer surface.

<Electroconductive Support>

A material forming the electroconductive support can be appropriatelyselected and used from materials known in the field ofelectrophotographic electroconductive members and materials that can beused as such electroconductive members. Examples thereof include metalsor alloys such as aluminum, stainless steel, electroconductive syntheticresins, iron, and copper alloys. Further, these may be subjected to anoxidation treatment or a plating treatment with chromium, nickel, or thelike. Either electroplating or electroless plating can be used as thetype of plating. From the viewpoint of dimensional stability, theelectroless plating is preferable. Examples of the electroless platingused here include nickel plating, copper plating, gold plating, andplating for other various alloys. The plating thickness is preferably0.05 μm or more, and in consideration of the balance between workingefficiency and rust prevention ability, the plating thickness ispreferably from 0.1 to 30 μm. The cylindrical shape of the support maybe a solid cylindrical shape or a hollow cylindrical shape. An outerdiameter of this support is preferably in the range of from φ3 mm to φ10mm.

The presence of a medium resistance layer or an insulating layer betweenthe support and the electroconductive layer makes it impossible toquickly supply the electric charge after the electric charge has beenconsumed due to the discharge. Therefore, it is preferable to providethe electroconductive layer directly on the support, or to provide theelectroconductive layer on the outer periphery of the support throughonly an intermediate layer formed of a thin film and anelectroconductive resin layer such as a primer.

As the primer, known ones can be selected and used according to therubber material for forming the electroconductive layer and the materialof the support. Examples of the material for the primer includethermosetting resins and thermoplastic resins, and specifically,materials such as phenolic resins, urethane resins, acrylic resins,polyester resins, polyether resins, and epoxy resins can be used.

The impedance of the resin layer and the support is preferably in therange of from 1.0×10⁻⁵ to 1.0×10²Ω at a frequency of from 1.0×10⁻² Hz to1.0×10¹ Hz. In a case of the support and the resin layer whose impedancein the low frequency is in the above range, the electric charges can besufficiently supplied to the electroconductive layer, and a function, ofa matrix-domain structure contained in the electroconductive layer, ofsuppressing the discharge omission according to the first and secondrequirements is not hindered, which is preferable.

The impedance of the resin layer can be measured by the same method asthe above-described measurement of the slope of the impedance, exceptthat the electroconductive layer existing on the outermost surface ispeeled off. In addition, the impedance of the support can be measured bythe same method as the above-described measurement of impedance, withthe electroconductive layer or the coating layer formed of the resinlayer and the electroconductive layer peeled off before coating theresin layer or electroconductive layer, or after forming the chargingroller.

<Electroconductive Layer>

As the electroconductive member satisfying the <first requirement> andthe <second requirement>, for example, an electroconductive memberhaving an electroconductive layer satisfying the followingconfigurations (i) to (iii) is preferable.

(i) The volume resistivity of the matrix is more than 1.0×10¹² Ω·cm and1.0×10¹⁷ Ω·cm or less.(ii) The volume resistivity of the domain is 1.0×10¹ Ω·cm or more and1.0×10⁴ Ω·cm or less.(iii) The distance between the adjacent wall surfaces of the domain iswithin a range of from 0.2 μm or more and 2.0 μm or less.

The configurations (i) to (iii) will be described below.

FIG. 6 illustrates a partially sectional view of the electroconductivelayer in a direction perpendicular to the longitudinal direction of theelectroconductive roller. An electroconductive layer 6 has amatrix-domain structure having a matrix 6 a and a domain 6 b. The domain6 b includes electroconductive particles 6 c as an electronicelectroconductive agent.

In the electroconductive layer when a bias is applied between theelectroconductive support and the body to be charged in theelectroconductive member including the electroconductive layer in whichthe domain containing the electronic electroconductive agent isdispersed in the matrix, it is considered that the electric charges movefrom the electroconductive support side of the electroconductive layerto the opposite side, that is, to the outer surface side of theelectroconductive member as follows. That is, the electric charge isaccumulated near the interface with the matrix in the domain. Then, theelectric charge is sequentially transferred from the domain positionedon the electroconductive support side to the domain positioned on theside opposite to the electroconductive support side, and reaches thesurface on the side (hereinafter, also referred to as “the outer surfaceof the electroconductive layer”) opposite to the electroconductivesupport side of the electroconductive layer. At this time, when theelectric charges of all the domains move to the outer surface side ofthe electroconductive layer in one charging step, it takes time toaccumulate the electric charges in the electroconductive layer for thesubsequent charging step. That is, it becomes difficult to support ahigh-speed electrophotographic image forming process. Therefore, it ispreferable that the transfer of electric charges between domains doesnot occur simultaneously even when a bias is applied. Further, even in ahigh frequency region where the movement of electric charges isrestricted, it is effective to accumulate a sufficient amount ofelectric charges in the domain in order to discharge a sufficient amountof electric charges in one discharge.

As described above, in order to suppress the simultaneous transfer ofelectric charges between the domains when a bias is applied and toaccumulate sufficient electric charges in the domains, it is preferablethat the volume resistivity of the matrix is set to be more than1.0×10¹² Ω·cm and 1.0×10¹⁷ Ω·cm or less (configuration (i)), and thevolume resistivity of the domain is set to be 1.0×10¹ Ω·cm or more and1.0×10⁴ Ω·cm or less (configuration (ii)), and the distance betweenadjacent wall surfaces between domains is set to be within a range of0.2 μm or more and 2.0 μm or less (configuration (iii)).

<Configuration (i)>

Volume Resistivity of Matrix;

By setting the volume resistivity of the matrix to be more than 1.0×10¹²Ω·cm and 1.0×10¹⁷ Ω·cm or less, it is possible to prevent the electriccharge from circumventing the domain and moving in the matrix. Inaddition, it is possible to prevent the state as if an electroconductivepath communicating with the electroconductive layer is formed when theelectric charges accumulated in the domain leaks into the matrix.

Regarding the <first requirement>, the present inventors consider thatin order to move the electric charges through the domain even in theelectroconductive layer under application of a high-frequency bias, aconfiguration in which the region (domain) where the electric chargesare sufficiently accumulated is divided by an electrically insulatingregion (matrix) is effective. Then, by setting the volume resistivity ofthe matrix to be within the range of the high resistance region asdescribed above, it is possible to retain sufficient electric charges atan interface with each domain, and it is possible to suppress electriccharge leakage from the domain.

Further, it has been found that it is effective to limit a movement pathof the electric charge to a path with a domain interposed in order toobtain an electroconductive layer satisfying the <second requirement>.By suppressing the leakage of the electric charges from the domains tothe matrix and limiting a transport path of the electric charges to apath with domains interposed, the density of the electric chargesexisting in the domains can be improved, and thus the electric charge ineach domain can be improved to further increase the filling amount. Withthis, it is possible to improve the total number of electric chargesthat can be related to the discharge on the surface of the domain as anelectroconductive phase that is a starting point of the discharge, andas a result, it is considered that the easiness of discharge from thesurface of the charging member can be improved.

In addition, the discharge generated from the outer surface of theelectroconductive layer includes a phenomenon in which electric chargesare extracted from the domain as the electroconductive phase by theelectric field, and at the same time, also includes a γ effect in whichpositive ions generated by ionization of air by an electric fieldcollide with the surface of the electroconductive layer in which anegative electric charge exists and release the electric charge from thesurface of the electroconductive layer. In the domain as theelectroconductive phase on the surface of the charging member, asdescribed above, the electric charges can be present at a high density.Therefore, it is presumed that when the positive ions collide with thesurface of the electroconductive layer due to the electric field, theefficiency of generating discharged electric charges can be improved,and it is possible to generate more discharged electric charges ascompared with the charging member in the related art.

Method for Measuring Volume Resistivity of Matrix;

The volume resistivity of the matrix can be measured with a fine probeafter thinning the electroconductive layer. Examples of means forthinning include a sharp razor, a microtome, and a focused ion beammethod (FIB).

When manufacturing thin pieces, it is necessary to eliminate theinfluence of domains and measure the volume resistivity of only thematrix, and therefore, it is necessary to manufacture the thin pieceswith a film thickness smaller the distance between domains measured inadvance with a scanning electron microscope (SEM) or a transmissionelectron microscope (TEM). Therefore, as means for thinning, meanscapable of manufacturing a very thin sample such as a microtome ispreferable.

In the measurement of the volume resistivity, first, one side of thethin piece is grounded, and then the locations of the matrix and thedomain in the thin piece are specified. These locations can be specifiedby a scanning probe microscope (SPM), an atomic force microscope (AFM),or the like by means capable of measuring the volume resistivity orhardness distribution of the matrix and domains. Then, a probe isbrought into contact with the matrix, a DC voltage of 50 V is appliedfor five seconds, the arithmetic average value of the ground currentvalue for five seconds is measured, and the electrical resistivity iscalculated by dividing the arithmetic average value by the voltage.Then, the film thickness of the thin piece may be converted into thevolume resistivity. At this time, means capable of measuring the shapesuch as SPM or AFM of the thin piece is preferable because the filmthickness of the thin piece can be measured and the volume resistivitycan be measured.

The volume resistivity of the matrix in the cylindricalelectroconductive member can be measured by dividing theelectroconductive layer into four sections in the circumferentialdirection, cutting out one thin sample from each of the five dividedregion in the longitudinal direction to obtain the above measurementvalues, and then calculating the arithmetic average value of the volumeresistivity of 20 samples in total.

<Configuration (ii)>

Volume Resistivity of Domain;

The volume resistivity of the domain is preferably 1.0×10¹ Ω·cm or moreand 1.0×10⁴ Ω·cm or less. By making the volume resistivity of the domainlower, it is possible to more effectively limit the transport path ofthe electric charges to the path with domains interposed whilesuppressing unwanted transfer of the electric charges in the matrix.

Further, the volume resistivity of the domain is more preferably 1.0×10²Ω·cm or less. By reducing the volume resistivity of the domain to theabove range, the amount of electric charges moving in the domain can bedramatically improved. Therefore, the impedance of the electroconductivelayer at a frequency of from 1.0×10⁻² Hz to 1.0×10¹ Hz can be controlledto be in a lower range of 1.0×10⁵Ω or lower so that the transport pathof the electric charges can be more effectively limited to the domain.

The volume resistivity of the domain is adjusted by adjusting theelectroconductivity of the rubber component of the domain to apredetermined value by using an electroconductive agent.

As the rubber material for the domain, a rubber composition containing arubber component for the matrix can be used, and it is more preferablethat a difference in solubility parameter (SP value) with the rubbermaterial forming the matrix to form the matrix-domain structure is 0.4(J/cm³)^(0.5) or more and 5.0 (J/cm³)^(0.5) or less, and isparticularly, 0.4 (J/cm³)^(0.5) or more and 2.2 (J/cm³)^(0.5) or less.

The volume resistivity of the domain can be adjusted by appropriatelyselecting the type of electronic electroconductive agent and theadditional amount thereof. As an electroconductive agent used to controlthe volume resistivity of the domain to be 1.0×10¹ Ω·cm or more and1.0×10⁴ Ω·cm or less, an electronic electroconductive agent that cangreatly change the volume resistivity from high resistance to lowresistance depending on the amount of dispersion is preferable.

Examples of the electronic electroconductive agent blended in the domaininclude oxides such as carbon black, graphite, titanium oxide, and tinoxide; metals such as Cu and Ag; and particles whose surface is coatedwith an oxide or metal to be electrically conductive. Further, ifnecessary, two or more types of these electroconductive agents may beused in an appropriate amount.

Among the above-mentioned electronic electroconductive agents, it ispreferable to use electroconductive carbon black, which has highaffinity with rubber and can easily control the distance between theelectronic electroconductive agents. The type of carbon black blended inthe domain is not particularly limited. Specific examples thereofinclude gas furnace black, oil furnace black, thermal black, lamp black,acetylene black, and Ketjen black.

Among these, electroconductive conductive carbon black having a DBP oilabsorption of 40 cm³/100 g or more and 170 cm³/100 g or less, which canimpart high electroconductive conductivity to the domain, can bepreferably used.

The electronic electroconductive agent such as electroconductiveconductive carbon black is preferably blended in the domain in an amountof 20 parts by mass or more and 150 parts by mass or less with respectto 100 parts by mass of the rubber component contained in the domain. Aparticularly preferable blending ratio is 50 parts by mass or more and100 parts by mass or less. The content of the electroconductiveconductive agent in these ratios is preferably such that a large amountof the electroconductive conductive agents are blended as compared witha general electrophotographic electroconductive member. As a result, thevolume resistivity of the domain can be easily controlled to be withinthe range of 1.0×10¹ Ω·cm or more and 1.0×10⁴ Ω·cm or less.

Further, if necessary, a filler, a processing aid, a cross-linking aid,a cross-linking accelerator, an anti-aging agent, a cross-linkingaccelerator, a cross-linking retarder, a softener, a dispersant, acolorant, and the like, which are generally used as a blending agent forrubber, may be added to the rubber composition for domains within arange that does not impair the effects of the present disclosure.

Method for Measuring Volume Resistivity of Domain;

The measurement of the volume resistivity of the domain may be performedby the same method as the above-described method for measuring thevolume resistivity of the matrix, except that the measurement point ischanged to a location corresponding to the domain and the appliedvoltage at the time of measuring the current value is changed to 1 V.

Here, the volume resistivity of the domain is preferably uniform. Inorder to improve the uniformity of the volume resistivity of thedomains, it is preferable to make the amount of the electronicelectroconductive agent in each domain uniform. This can furtherstabilize the discharge from the outer surface of the electroconductivemember to the body to be charged.

Specifically, with respect to each cross-sectional area of each domainthat appears in the cross section in the thickness direction of theelectroconductive layer, when moieties of the electronicelectroconductive agent contained in each domain, for example, astandard deviation of the ratio of a total cross-sectional area of theelectroconductive particles to the cross-sectional area of the domain isdefined as σr and a mean value is defined as μr, a coefficient ofvariation σr/μr is preferably 0 or more and 0.4 or less.

Since σr/μr is 0 or more and 0.4 or less, a method for reducing thevariation in the number or amount of the electroconductive agentcontained in each domain can be used. By imparting the uniformity of thevolume resistivity of the domain based on such an index, it is possibleto suppress the electric field concentration in the electroconductivelayer and reduce the presence of the matrix to which the electric fieldis locally applied. With this, the electroconductivity in the matrix canbe reduced as much as possible.

More preferable σr/μr is 0 or more and 0.25 or less, and it is possibleto more effectively suppress the electric field concentration in theelectroconductive layer, and further reduce the impedance at 1.0×10⁻² Hzto 1.0×10¹ Hz to 1.0×10⁵Ω or less.

In order to improve the uniformity of the volume resistivity of thedomains, it is preferable to increase the blending amount of carbonblack with respect to the second rubber in the step of preparing arubber mixture for forming a domain (CMB) described below.

Method for Measuring Uniformity of Volume Resistivity of Domain;

Since the uniformity of the volume resistivity of the domain isdependent on the amount of the electronic electroconductive agent in thedomain, it can be evaluated by measuring the variation in the amount ofthe electronic electroconductive agent in each domain.

First, a slice is available from the same method as the method formeasuring the volume resistivity of the matrix described above. Then, afracture surface is formed by means such as a freeze fracture method, across polisher method, and a focused ion beam method (FIB). Inconsideration of the smoothness of the fracture surface and thepretreatment for observation, the FIB method is preferable. Further, inorder to suitably observe the matrix-domain structure, a pretreatmentsuch as a dyeing treatment or a vapor deposition treatment may beperformed to obtain a favorable contrast between the domain as anelectroconductive phase and the matrix as an insulating phase.

The existence of the matrix-domain structure is checked by observing theslice subjected to the formation of the fracture surface and thepretreatment with a scanning electron microscope (SEM) or a transmissionelectron microscope (TEM). Among these, it is preferable to performobservation with SEM at 1000 to 100,000 times in terms of accuracy ofquantification of domain area.

The uniformity of low volume efficiency of the domains is preferablymeasured by quantifying a captured image of the fracture surface showingthe matrix-domain structure. Image processing software (for example,“ImageProPlus”, available from Media Cybernetics, Inc.) is used for thefracture surface image obtained by observation with SEM to perform 8-bitgrayscale conversion, thereby obtaining a 256-tone monochrome image.Next, the black and white of the image is inverted so that the domain inthe fracture surface becomes white, and binarization is performed. Then,a cross-sectional area S of the domain and a cross-sectional area Sc ofthe part made of the electroconductive agent in each domain arecalculated by using a counting function in the image processing softwarefor the binarized image. Then, the standard deviation σr and the averagevalue μr of the area ratio Sc/S in the domain of the electronicelectroconductive agent may be calculated, and σr/μr may be calculatedas an index of the uniformity of the volume resistivity of the domain.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and L/4 fromboth ends of the electroconductive layer toward the center. For each ofthe obtained cross sections, a 15 μm square observation area is obtainedat any three locations in the thickness region from the outer surface ofthe electroconductive layer to the depth of from 0.1 T to 0.9 T in asupport direction. σr/μr may be calculated as an index of the uniformityof the volume resistivity of the domain by binarizing and quantifyingthe observation area by the above method, and the arithmetic averagevalue of the measurement values from the nine observation areas in totalmay be quantified as an index of the uniformity of domain size.

<Configuration (iii)>

Distance Between Adjacent Wall Surfaces Between Domains (HereinafterAlso Referred to as “Inter-Domain Surface Distances”)

The inter-domain surface distances is preferably 0.2 μm or more and 2.0μm or less.

In the matrix having the volume resistivity according to theconfiguration (i), the electroconductive layer in which the domain ofthe volume resistivity according to the configuration (ii) is dispersedhas the inter-domain surface distances preferably 2.0 μm or less, andparticularly 1.0 μm or less in order to satisfy the <secondrequirement>. On the other hand, the inter-domain surface distances ispreferably 0.2 μm or more, and particularly preferably 0.3 μm or more inorder to accumulate sufficient electric charges in the domains by surelydividing the domains from each other in the insulating region.

Method for Measuring Inter-Domain Surface Distances;

The method for measuring the inter-domain surface distances may beperformed as follows.

First, a slice is available from the same method as the method formeasuring the volume resistivity of the matrix described above. Then, afracture surface is formed by means such as a freeze fracture method, across polisher method, and a focused ion beam method (FIB). Inconsideration of the smoothness of the fracture surface and thepretreatment for observation, the FIB method is preferable. Further, inorder to suitably observe the matrix-domain structure, a pretreatmentsuch as a dyeing treatment or a vapor deposition treatment may beperformed to obtain a favorable contrast between an electroconductivephase and an insulating phase.

The existence of the matrix-domain structure is checked by observing theslice subjected to the formation of the fracture surface and thepretreatment with a scanning electron microscope (SEM) or a transmissionelectron microscope (TEM). Among these, it is preferable to performobservation with SEM at 1000 to 100,000 times in terms of accuracy ofquantification of domain area.

The inter-domain surface distances is preferably measured by quantifyinga captured image of the fracture surface showing the matrix-domainstructure. Image processing software (for example, “Luzex” (productname, available from Nireco)) is used for the fracture surface imageobtained by observation with SEM to perform 8-bit grayscale conversion,thereby obtaining a 256-tone monochrome image. Next, the black and whiteof the image is inverted so that the domain in the fracture surfacebecomes white, and binarization is performed. Next, the distance betweenthe wall surfaces of the domain size group in the image is calculated.The distance between the wall surfaces at this time is the shortestdistance between the adjacent domains.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and L/4 fromboth ends of the electroconductive layer toward the center. For each ofthe obtained cross sections, 50 μm square observation areas are obtainedat any three locations in the thickness region from the outer surface ofthe electroconductive layer to the depth of from 0.1 T to 0.9 T in asupport direction, and the inter-domain surface distances observed ineach of the observation areas may be measured. Since it is necessary toobserve a plane including the outer surface of the electroconductivelayer from the support, which is the movement direction of electriccharges, a slice is cut in the direction in which a cross sectionincluding a normal line with a central axis of the support as a startingpoint can be observed.

Uniformity of Inter-Domain Surface Distances;

With regard to the above configuration (iii), it is more preferable thatthe distribution of the inter-domain surface distances is uniform. Theuniform distribution of the distance between the domains allows somelocations with the distance between the domains to be formed locally inthe electroconductive layer, and thus it is possible to reduce thephenomenon that the easiness of discharge is suppressed when, forexample, there is a place where the supply of electric charges isdelayed as compared to the surroundings.

In the cross section to which the electric charges are transported, thatis, in the cross section of the electroconductive layer in the thicknessdirection as illustrated in FIG. 8B, when 50 μm square observation areais obtained at any three locations in the thickness region from theouter surface of the electroconductive layer to the depth of from 0.1 Tto 0.9 T in a support direction, the variation coefficient am/Dm ispreferably 0 or more and 0.4 or less using the average value Dm of theinter-domain surface distances and the variation am of the inter-domainsurface distances in the observation area.

Method for Measuring Uniformity of Inter-Domain Surface Distances;

The uniformity of the inter-domain surface distances can be measured byquantifying the image obtained by direct observation of the fracturesurface, similar to the measurement of the inter-domain surfacedistances described above.

The measurement may be performed in such a manner that by using imageprocessing software such as LUZEX (available from Nireco Corporation)for the binarized image of the fracture surface obtained by themeasurement of the inter-domain surface distances, the average value Dmof the inter-domain surface distances of the domain size group in theimage and the standard deviation am of Dm may be calculated, and am/Dmmay be calculated as an index of the uniformity of the inter-domainsurface distances.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and at L/4from both ends of the electroconductive layer toward the center. Foreach of the obtained cross sections, a 50 μm square observation area isobtained at any three locations in the thickness region from the outersurface of the electroconductive layer to the depth of from 0.1 T to 0.9T in a support direction. σm/Dm of the inter-domain surface distancesmay be calculated by binarizing and quantifying the observation area bythe above method, and the arithmetic average value of the measurementvalues from the nine observation areas in total may be quantified as anindex of the uniformity of the inter-domain surface distances.

The electroconductive member according to this aspect can be formed, forexample, by a method including the following steps (i) to (iv).

Step (i): a step of preparing a rubber mixture for forming a domainwhich contains carbon black and a second rubber (hereinafter, alsoreferred to as “CMB”);Step (ii): a step of preparing a rubber mixture for forming a matrixwhich contains a first rubber (hereinafter, also referred to as “MRC”);Step (iii): a step of kneading CMB and MRC to prepare a rubber mixturehaving a matrix-domain structure.Step (iv): a step of forming a layer of the rubber mixture prepared inthe step (iii) on an electroconductive support directly or throughanother layer, and curing the layer of the rubber composition to form anelectroconductive layer according to this aspect.

The configurations (i) to (iii) can be controlled by, for example,selecting the material used in each of the steps and adjusting themanufacturing conditions. This will be described below.

First, regarding the configuration (i), the volume resistivity of thematrix is determined by the composition of the MRC.

As the first rubber used for MRC, at least one type of rubber having lowelectroconductivity such as a natural rubber, a butadiene rubber, abutyl rubber, an acrylonitrile butadiene rubber, a urethane rubber, asilicone rubber, a fluorine rubber, an isoprene rubber, a chloroprenerubber, a styrene-butadiene rubber, an ethylene-propylene rubber, and apolynorbornene rubber may be used. In addition, assuming that the volumeresistivity of the matrix can be within the above range, if necessary, afiller, a processing aid, a cross-linking agent, a cross-linking aid, across-linking accelerator, a cross-linking accelerator, a cross-linkingretarder, an antioxidant, a softener, a dispersant, and a colorant areadded to MRC. On the other hand, it is preferable that the MRC does notcontain an electronic electroconductive agent such as carbon black inorder to keep the volume resistivity of the matrix within the aboverange.

Further, the configuration (ii) can be adjusted by the amount of theelectronic electroconductive agent in the CMB. For example, whenexemplifying a case of using electroconductive carbon black having DBPoil absorption of 40 cm³/100 g or more and 170 cm³/100 g or less as anexample of the electronic electroconductive agent, the configuration(ii) can be achieved by preparing the CMB so as to contain theelectroconductive carbon black in an amount of 40% by mass or more and200% by mass or less based on the total mass of CMB.

Further, regarding the configuration (iii), it is effective to controlthe following four matters (a) to (d).

(a) Difference in interfacial tension a between CMB and MRC;(b) Ratio (ηm/ηd) of MRC viscosity (ηm) to CMB viscosity (ηd);(c) Shear rate (γ) at the time of kneading CMB and MRC in Step (iii),and energy amount (EDK) at the time of shear(d) Volume fraction of CMB to MRC in step (iii).

(a) Difference in Interfacial Tension Between CMB and MRC

Generally, when two types of incompatible rubbers are mixed, phaseseparation occurs. This is because the interaction between the samepolymers is stronger than the interaction between the differentpolymers, so that the same polymers agglomerate to reduce the freeenergy and to be stabilized. Since the interface of a phase-separatedstructure comes into contact with a different polymer, the free energybecomes higher than that of the inside which is stabilized by theinteraction between the same molecules. As a result, in order to reducethe free energy of the interface, interfacial tension is generated toreduce the area in contact with the different polymer. When theinterfacial tension is small, the different polymers tend to be mixedmore uniformly in order to increase entropy. The state of beinguniformly mixed means dissolution, and a SP value (solubility parameter)which is a measure of solubility and the interfacial tension tend to becorrelated.

That is, it is considered that a difference in the interfacial tensionbetween CMB and MRC and the interfacial tension between CMB and MRCcorrelate with the SP value difference of the rubber contained in each.As the first rubber in MRC and the second rubber in CMB, it ispreferable to select a rubber in which the difference in the absolutevalue of the solubility parameter is 0.4 (J/cm³)^(0.5) or more and 5.0(J/cm³)^(0.5) or less, and particularly 0.4 (J/cm³)^(0.5) or more and2.2 (J/cm³)^(0.5) or less. Within this range, a stable phase-separatedstructure can be formed, and a domain diameter D of CMB can be reduced.Here, specific examples of the second rubber that can be used for CMBinclude a natural rubber (NR), an isoprene rubber (IR), a butadienerubber (BR), a styrene-butadiene rubber (SBR), a butyl rubber (IIR), anethylene-propylene rubber (EPM, EPDM), a chloroprene rubber (CR), anitrile rubber (NBR), a hydrogenated nitrile rubber (H-NBR), a siliconerubber, and a urethane rubber (U). At least one of these can be used.

The thickness of the electroconductive layer is not particularly limitedas long as the intended function and effect of the electroconductivemember can be obtained. The thickness of the electroconductive layer ispreferably 1.0 mm or more and 4.5 mm or less.

<Method for Measuring SP Value>

The SP value can be accurately calculated by creating a calibrationcurve using a material having a known SP value. A materialmanufacturer's catalog value can also be used for this known SP value.

For example, NBR and SBR do not depend on the molecular weight, and theSP value is almost determined by the content ratio of acrylonitrile andstyrene. Therefore, regarding the rubber constituting the matrix and thedomain, using an analysis method such as pyrolysis gas chromatography(Py-GC) and solid-state NMR, by analyzing the content ratio ofacrylonitrile or styrene, the SP value can be calculated from thecalibration curve obtained from a material having a known SP value.Further, regarding the isoprene rubber, the SP value is determined by anisomer structure such as 1,2-polyisoprene, 1,3-polyisoprene,3,4-polyisoprene, cis-1,4-polyisoprene, and trans-1,4-polyisoprene.Therefore, similar to SBR and NBR, the isomer content ratio can beanalyzed by Py-GC, solid NMR, and the like, and the SP value can becalculated from a material having a known SP value.

(b) Viscosity Ratio of CMB and MRC

The closer the viscosity ratio (ηd/ηm) of CMB and MRC is to 1, thesmaller the maximum ferret diameter of the domain can be made.Specifically, the viscosity ratio is preferably 1.0 or more and 2.0 orless. The viscosity ratio of CMB and MRC can be adjusted by selectingthe Mooney viscosity of the raw material rubber used for CMB and MRC,and by mixing the types and amounts of fillers. It is also possible toadd a plasticizer such as a paraffin oil to the extent that theformation of the phase-separated structure is not hindered. In addition,the viscosity ratio can be adjusted by adjusting the temperature at thetime of kneading. The viscosity of the rubber mixture for forming thedomain and the rubber mixture for forming the matrix can be obtained bymeasuring the Mooney viscosity ML(1+4) at the rubber temperature at thetime of kneading based on JIS K6300-1:2013.

(c) Shear Rate at the Time of Kneading MRC and CMB, and Energy Amount atthe Time of Shear

The higher the shear rate at the time of kneading MRC and CMB and thelarger the energy amount at the time of shear, the smaller theinter-domain surface distances can be made.

The shear rate can be increased by increasing the inner diameter of astirring member such as a blade or a screw of a kneading machine,reducing a gap between the end surface of the stirring member and theinner wall of the kneading machine, or increasing the rotation speed. Inorder to increase the energy at the time of shear, it is possible toincrease the rotation speed of the stirring member and the viscosity ofthe first rubber in CMB and the second rubber in MRC.

(d) Volume Fraction of CMB to MRC

The volume fraction of CMB to MRC correlates with the collisioncoalescence probability of the rubber mixture for forming a domain to arubber mixture for forming a matrix. Specifically, when the volumefraction of the rubber mixture for forming a domain to the rubbermixture for forming a matrix is reduced, the collision coalescenceprobability of the rubber mixture for forming a domain and the rubbermixture for forming a matrix is reduced. In other words, the distancebetween the domains can be reduced by reducing the volume fraction ofthe domains in the matrix within the range where the requiredelectroconductivity can be obtained. The volume fraction of CMB to MRCis preferably 15% or more and 40% or less.

Further, in the electroconductive layer of the electroconductive memberaccording to the present aspect, when the length of theelectroconductive layer in the longitudinal direction is defined as L,for each of the cross sections in the thickness direction of theelectroconductive layer at three locations of the center of theelectroconductive layer in the longitudinal direction and L/4 from bothends of the electroconductive layer toward the center, when a 15 μmsquare observation area is placed at any three locations in thethickness region from the outer surface of an elastic layer to the depthof from 0.1 T to 0.9 T, it is preferable that among the domains observedin each of the observation areas, 80% by number or more of the domainssatisfy the following configurations (iv) and (v).

Configuration (iv)

The ratio of the cross-sectional area of the electroconductive particlescontained in the domain to the cross-sectional area of the domain is 20%or more.

Configuration (v)

When defining a perimeter of the domain as A, and defining an envelopeperimeter of the domain as B, A/B is 1.00 or more and 1.10 or less.

The above configurations (iv) and (v) can be said to be regulationsregarding the shape of the domain. The “shape of domain” is defined as across-sectional shape of the domain appearing in the cross section ofthe electroconductive layer in the thickness direction. In a case of acylindrical charging member, when a length of the electroconductivelayer in the longitudinal direction is defined as L and a thickness ofthe electroconductive layer is defined as T, cross sections of theelectroconductive layer in the thickness direction, as illustrated inFIG. 8B, are obtained at three locations of the center of theelectroconductive layer in the longitudinal direction and at L/4 fromboth ends of the electroconductive layer toward the center. For each ofthe obtained cross sections, a 15 μm square observation area is placedat any three locations in the thickness region from the outer surface ofthe electroconductive layer to the depth of from 0.1 T to 0.9 T in asupport direction. The domain shape is defined by the shape of eachdomain observed in each of the observation areas.

It is preferable that the shape of the domain is such that theperipheral surface thereof has no irregularities. By reducing the numberof irregular structures related to the shape, it is possible to reducethe non-uniformity of the electric field between the domains, that is,to reduce the number of locations where the electric field isconcentrated and reduce the phenomenon of unnecessary electric chargetransport in the matrix.

The present inventors have found that the amount of electroconductiveparticles contained in one domain affects an outer shape of the domain.That is, it has been found that the outer shape of the domain becamecloser to a sphere as the filling amount of the electroconductiveparticles in one domain is increased. The larger the number of domainsclose to a sphere, the smaller the concentration point of electrontransfer between domains can be reduced. Then, according to the studiesby the present inventors, the reason is not clear, but based on thecross-sectional area of one domain, the domain in which the ratio of thetotal cross-sectional area of the electroconductive particles observedin the cross section is 20% or more can be made closer to a sphere. As aresult, an outer shape that can significantly alleviate theconcentration of electron transfer between domains can be obtained,which is preferable. Specifically, the ratio of the cross-sectional areaof the electroconductive particles contained in the domain to thecross-sectional area of the domain is preferably 20% or more.

The present inventors have found that it is preferable to satisfy thefollowing Equation (5) relating to a shape in which the circumferentialsurface of the domain has no irregularities.

1.00≤AB≤1.10  (5)

(A: perimeter of domain, B: envelope perimeter of domain)

Equation (5) indicates a ratio of the perimeter A of the domain to theenvelope perimeter B of the domain. Here, the envelope perimeter is aperimeter when protrusion portions of a domain 71 observed in theobservation area are connected, as illustrated in FIG. 7.

The ratio of the perimeter of the domain to the envelope perimeter ofthe domain has a minimum value of 1, and a state where the value is 1indicates that the domain has a shape such as a perfect circle or anellipse in which there is no recess in the cross-sectional shape. Whenthese ratios exceed 1.1, large irregularities are present in the domain,that is, anisotropy of electric field is exhibited.

<Method for Measuring Each Parameter Related to Domain Shape>

First, a slice is available from the same method as the method formeasuring the volume resistivity of the matrix described above. However,as described below, it is necessary to create a slice by a cross sectionperpendicular to the longitudinal direction of the electroconductivemember and evaluate the shape of the domain in the fracture surface ofthe slice. The reason for this will be described below.

FIGS. 8A and 8B are diagrams illustrating the shape of anelectroconductive member 81 as three axes, specifically, threedimensions of X, Y, and Z axes. FIGS. 8A and 8B, the X axis indicates adirection parallel to the longitudinal direction (axial direction) ofthe electroconductive member, and the Y axis and the Z axis indicatedirections perpendicular to the axial direction of the electroconductivemember.

FIG. 8A illustrates an image view of cutting out the electroconductivemember at a cross section 82 a parallel to an XZ plane 82 with respectto the electroconductive member. The XZ plane can rotate 360° about theaxis of the electroconductive member. When considering that theelectroconductive member is rotated while being in contact with thephotosensitive drum and passing through the gap with the photosensitivedrum, the cross section 82 a parallel to the XZ plane 82 means a planeon which the discharge simultaneously occurs at a certain timing. Thesurface potential of the photosensitive drum is formed by passing aplane corresponding to a certain amount of the cross section 82 a.

Therefore, in order to evaluate the shape of the domain, which iscorrelated with the electric field concentration in theelectroconductive member, it is necessary to perform the evaluation in across section parallel to the YZ plane 83 that is perpendicular to theaxial direction of the electroconductive member, and that can evaluatethe domain shape including a certain amount of cross section 82 a,instead of the analysis of the cross section, such as the cross section82 a, in which the discharge simultaneously occurs at a certain moment.In this evaluation, when the length of the electroconductive layer inthe longitudinal direction is defined as L, total three locations of across section 83 b at the center of the electroconductive layer in thelongitudinal direction, and two cross sections (83 a and 83 c) at L/4from both ends of the electroconductive layer toward the center areselected.

Regarding the observation positions of the cross sections 83 a to 83 c,when the thickness of the electroconductive layer is T, if theobservation area having a 15 μm square is placed at any three locationsin the thickness region from the outer surface of each slice to a depthof 0.1 T or more and 0.9 T or less, the measurement may be performed ina total of nine observation areas.

The fracture surface can be formed by means such as a freeze fracturemethod, a cross polisher method, and a focused ion beam method (FIB). Inconsideration of the smoothness of the fracture surface and thepretreatment for observation, the FIB method is preferable. Further, inorder to suitably observe the matrix-domain structure, a pretreatmentsuch as a dyeing treatment or a vapor deposition treatment may beperformed to obtain a favorable contrast between an electroconductivephase and an insulating phase.

The matrix-domain structure can be observed using a scanning electronmicroscope (SEM) or a transmission electron microscope (TEM) on theslice subjected to the formation of the fracture surface and thepretreatment. Among these, it is preferable to perform observation withSEM at 1000 to 100,000 times in terms of accuracy of quantification ofdomain area.

The perimeter and the envelope perimeter of the domain, and the numberof domains can be measured by quantifying the captured image asdescribed above. Using the image processing such as ImageProPlus(available from Media Cybernetics, Inc.) for the fracture surface imageobtained by SEM observation, 15 μm square analysis region is extractedfrom each of the nine images obtained at each observation position toperform 8-bit grayscale conversion, thereby obtaining a 256-tonemonochrome image. Then, the black and white of the image is inverted sothat the domain in the fracture surface becomes white, and binarized toobtain a binarized image for analysis.

<<Method for Measuring Cross-Sectional Area Ratio μr ofElectroconductive Particles in Domain>>

The cross-sectional area ratio of the electroconductive particles in thedomain can be measured by quantifying the binarized image. Across-sectional area S of the domain and a sum Sc of a cross-sectionalarea of the part made of the electroconductive agent in each domain arecalculated by using a counting function in the image processing software“ImageProPlus” (available from Media Cybernetics, Inc.) for thebinarized image. Then, the arithmetic average value μr (%) of Sc/S maybe calculated.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 6, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and at L/4from both ends of the electroconductive layer toward the center. Foreach of the obtained cross sections, the above measurement may beperformed in 15 μm square observation areas at any three locations inthe thickness region from the outer surface of the electroconductivelayer to the depth of from 0.1 T to 0.9 T in a support direction, sothat the cross-sectional area ratio is calculated from the arithmeticaverage value of the measured values from a total of nine regions.

<<Method for Measuring Perimeter A and Envelope Perimeter B of theDomain>>

The perimeter and the envelope perimeter of the domain, and the numberof domains can be measured by quantifying the binarized image asdescribed above. By using the counting function of the image processingsoftware “ImageProPlus” (available from Media Cybernetics, Inc.) for thebinarized image, the perimeter A of the domain and the envelopeperimeter B of the domain of the domain size group in the image may becalculated so calculate the arithmetic average value of the perimeterratio A/B of the domain.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and at L/4from both ends of the electroconductive layer toward the center. Foreach of the obtained cross sections, the above measurement may beperformed in 15 μm square observation areas at any three locations inthe thickness region from the outer surface of the electroconductivelayer to the depth of from 0.1 T to 0.9 T in a support direction, sothat the cross-sectional area ratio is calculated from the arithmeticaverage value of the measured values from a total of nine regions.

<<Method for Measuring Shape Index of Domain>>

The shape index of the domain may be calculated by calculating thenumber percent of the domain group, in which μr (%) is 20% or more andthe perimeter ratio AB of the domain satisfies the above Equation (5),with respect to the total number of domains. For the binarized image,using the count function of the image processing software “ImageProPlus”(Media Cybernetics Co., Ltd.), the number in the binarized image of thedomain group may be calculated to further obtain the number percent ofdomains that satisfy μr≥20 and the above Equation (5).

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and at L/4from both ends of the electroconductive layer toward the center. Foreach of the obtained cross sections, the above measurement may beperformed in 15 μm square observation areas at any three locations inthe thickness region from the outer surface of the electroconductivelayer to the depth of from 0.1 T to 0.9 T in a support direction, sothat the cross-sectional area ratio is calculated from the arithmeticaverage value of the measured values from a total of nine regions.

As defined in configuration (iv), by filling the domain withelectroconductive particles at a high density, the outer shape of thedomain can be made closer to a sphere, and the irregularities can bemade small as defined in configuration (v).

Particularly, carbon black having a DBP oil absorption of 40 cm³/100 gor more and 80 cm³/100 g or less can be preferably used as theelectroconductive particles in order to obtain a domain with which theelectroconductive particles are filled at a high density, as defined inthe configuration (iv). The DBP oil absorption (cm³/100 g) means avolume of dibutyl phthalate (DBP) capable of adsorbing 100 g of carbonblack, and is measured based on Japanese Industrial Standards (JIS) K6217-4:2017 (carbon black for rubber-basic characteristics—Part 4:Method for obtaining oil absorption (including compressed sample)).Generally, carbon black has a tufted higher-order structure in whichprimary particles having an average particle size of 10 nm or more and50 nm or less are aggregated. This tufted higher-order structure iscalled a structure, and a degree thereof is quantified by the DBP oilabsorption (cm³/100 g).

Generally, carbon black having a developed structure has a highreinforcing property to rubber, the carbon black is poorly taken intothe rubber, and the shear torque at the time of kneading is extremelyhigh. Therefore, it is difficult to increase the filling amount in thedomain.

On the other hand, the electroconductive carbon black having the DBP oilabsorption within the above range has a less-developed structure, sothat the carbon blacks are less aggregated and has good dispersibilityin rubber. Therefore, the filling amount in the domain can be increased,and as a result, the outer shape of the domain can be more easily madecloser to a sphere.

Further, in the carbon black having a developed structure, the carbonblacks are easily aggregated with each other, and the aggregates arelikely to be a lump having a large irregular structure. When such anaggregate is included in the domain, it is difficult to obtain thedomain related to the requirement (v). The formation of the aggregatemay affect the shape of the domain to form an irregular structure. Onthe other hand, the electroconductive carbon black having the DBP oilabsorption within the above range is difficult to form aggregates, andis therefore effective in creating the domain relating to therequirement (v).

<Domain Size>

The domain according to the present aspect, an average of the maximumferret diameter (hereinafter, also simply referred to as “domaindiameter”) L of the domain included in each of the domains satisfyingthe above-mentioned configuration (iv) and configuration (v) ispreferably 0.1 μm or more and 5.0 μm or less.

When setting the average value of the domain diameter L to be 0.1 μm ormore, it is possible to effectively limit the path through whichelectric charges move to the intended path in the electroconductivelayer. Further, when setting the average value of the domain diameter Lto be 5.0 μm or less, the ratio of the surface area to the entire areaof the domain, that is, the specific surface area can be exponentiallyincreased, and the discharging efficiency of the electric charges fromthe domain can be dramatically improved. For the above reason, theaverage value of the domain diameter L is preferably 2.0 μm or less, andmore preferably 1.0 μm or less.

In order to further reduce the electric field concentration between thedomains, it is preferable that the outer shape of the domain is madecloser to a sphere. For that purpose, it is preferable that the domaindiameter can be made smaller within the above range. Examples of themethod include, in Step (iv), a method of controlling the domaindiameter of CMB to be small in a step of kneading MRC and CMB andperforming phase separation on MRC and CMB to prepare a rubber mixturein which the domain of CMB is formed in the matrix of MRC. When thedomain diameter of CMB is reduced, the specific surface area of CMB isincreased and the interface with the matrix is increased, and therefore,a tension acting to reduce the tension acts on the interface of thedomain of CMB. As a result, the outer shape of the domain of CMB iscloser to a sphere.

Here, regarding the factors that determine the domain diameter L in thematrix-domain structure formed when two incompatible polymers aremelt-kneaded, Taylor's Equation (Equation (6)), Wu's empirical Equation(Equations (7) and (8)), and Tokita's Equation (Equation (9)) are known.

Taylor's Equation

D=[C·σ/ηm·γ]·f(ηm/ηd)  (6)

Wu's empirical Equation

γ·D·ηm/σ=4(ηd/ηm)0.84·ηd/ηm>1  (7)

γ·D·ηm/σ=4(ηd/ηm)−0.84·ηd/ηm<1  (8)

Tokita's Equation

D=12·σ·φ/(π·η·γ)·(1+4·P·φ·EDK/(π·η·γ))  (9)

In Equations (6) to (9), D represents the maximum ferret diameter of thedomain of CMB, C represents a constant, σ represents interfacialtension, ηm represents the viscosity of the matrix, ηd represents theviscosity of the domain, and γ represents the shear rate, η representsthe viscosity of mixed system, P represents the collision coalescenceprobability, φ represents domain phase volume, and EDK represents domainphase cutting energy.

In order to equalize the inter-domain surface distances in relation tothe configuration (iii), it is effective to reduce the domain sandsaccording to the above Equations (6) to (9). Further, the matrix-domainstructure is also governed by where a kneading step is stopped in aprocess of the kneading step in which the raw material rubber of thedomain splits and the grain system gradually becomes smaller. Therefore,the uniformity of the inter-domain surface distances can be controlledby the kneading time in the kneading process and the kneading rotationspeed that is an index of the strength of the kneading, and the longerthe kneading time and the higher the kneading rotation speed, the moreuniform the inter-domain surface distances can be.

Uniformity of Domain Size;

It is preferable that the domain size is uniform, that is, the particlesize distribution is narrow. By evening out the distribution of the sizeof domains through which the electric charges pass in theelectroconductive layer, it is possible to suppress the concentration ofthe electric charges in the matrix-domain structure and effectivelyincrease the easiness of discharge across the entire surface of theelectroconductive member. In the cross section to which the electriccharges are transported, that is, in the cross section of theelectroconductive layer in the thickness direction as illustrated inFIG. 5, when 50 μm square observation area is obtained at any threelocations in the thickness region from the outer surface of theelectroconductive layer to the depth of from 0.1 T to 0.9 T in a supportdirection, the ratio σd/D (variation coefficient σd/D) of the standarddeviation σd of the domain size and the average value D of the domainsize is preferably 0 or more and 0.4 or less.

In order to improve the uniformity of the domain size, similar to themethod of improving the uniformity of the inter-domain surface distancesdescribed above, the uniformity of the domain size is also improved byreducing the domain size according to Equations (6) to (9). Further, thematrix-domain structure is also governed by where a kneading step isstopped in a process of the kneading step in which the raw materialrubber of the domain splits and the grain system gradually becomessmaller. Therefore, the uniformity of the domains size can be controlledby the kneading time in the kneading process and the kneading rotationspeed that is an index of the strength of the kneading, and the longerthe kneading time and the higher the kneading rotation speed, the moreuniform the domain size can be.

Method for Measuring Uniformity of Domain Size;

The uniformity of the domain size can be measured by quantifying theimage obtained by direct observation of the fracture surface, which isobtained by the same method as the measurement of the uniformity of theinter-domain surface distances described above.

Specifically, by using the counting function of the image processingsoftware “ImageProPlus” (available from Media Cybernetics, Inc.) for thebinarized image having the domain and the matrix, which is obtained bythe measurement of the inter-domain surface distances described above,the ratio ad/D between the standard deviation ad of the domain sizegroup and the average value D may be calculated.

In a case of the cylindrical charging member, the index of theuniformity of domain size can be quantified by calculating ad/D of theinter-domain surface distances on the normal line with the central axisof the support as the starting point.

In a case of a cylindrical charging member, when a length of theelectroconductive layer in the longitudinal direction is defined as Land a thickness of the electroconductive layer is defined as T, crosssections of the electroconductive layer in the thickness direction, asillustrated in FIG. 8B, are obtained at three locations of the center ofthe electroconductive layer in the longitudinal direction and L/4 fromboth ends of the electroconductive layer toward the center. For each ofthe obtained cross sections, a 50 μm square observation area is obtainedat any three locations in the thickness region from the outer surface ofthe electroconductive layer to the depth of from 0.1 T to 0.9 T in asupport direction. σd/D of the inter-domain surface distances may becalculated by binarizing and quantifying the observation area by theabove method, and the arithmetic average value of the measurement valuesfrom the nine observation areas in total may be quantified as an indexof the uniformity of the domain size.

<Method for Checking Matrix-Domain Structure>

The existence of the matrix-domain structure in the electroconductivelayer can be checked by manufacturing a thin piece from theelectroconductive layer and observing the fracture surface formed on thethin piece in detail.

Examples of means for thinning include a sharp razor, a microtome, and aFIB. Further, in order to more accurately observe the matrix-domainstructure, a pretreatment such as a dyeing treatment or a vapordeposition treatment may be performed on the thin piece for observationto obtain a favorable contrast between the domain as anelectroconductive phase and the matrix as an insulating phase.

The existence of matrix-domain structure can be checked by observing thefracture surface with a laser microscope, a scanning electron microscope(SEM) or a transmission electron microscope (TEM) on the thin piecesubjected to the formation of the fracture surface and the pretreatmentas necessary. As a method for easily and accurately checking asea-island structure, it is preferable to observe with a scanningelectron microscope (SEM).

After obtaining a thin piece of the electroconductive layer by themethod as described above and obtaining an image obtained by observingthe surface of the thin piece at a magnification of 1,000 to 10,000, theimage processing is performed by using the image processing software“ImageProPlus” (available from Media Cybernetics, Inc.) to perform 8-bitgrayscale conversion, thereby obtaining a 256-tone monochrome image.Next, the black and white of the image is inverted so that the domain inthe fracture surface becomes white, and binarized to obtain an analysisimage. The presence or absence of the matrix-domain structure may bedetermined based on the analysis image that has been image-processed ina state of distinguishing the domain and the matrix by binarization.

In a case where the analysis image has a structure in which domainsexist in an isolated state in the matrix as illustrated in FIG. 6, theexistence of the matrix-domain structure in the electroconductive layercan be checked. The isolated state of the domain may be a state in whicheach domain is disposed not connected to the other domain, the matrixcommunicates in the image, and the domain is divided by the matrix.Specifically, a state, in which when a region within 50 μm square in theanalysis image is defined as an analysis region, the number of domainsexisting in the isolated state as described above is 80 number % or morewith respect to the total number of domain groups that do not havecontact with a frame line of the analysis region, is defined as a statehaving a sea-island structure.

The checking as described above may be performed in such a manner thatthe electroconductive layer of the electroconductive member is equallydivided into five regions in the longitudinal direction, equally dividedinto four regions in the circumferential direction to manufacture aslice optionally from each region, 20 sections in total, and then theabove measurement is performed on the sections.

<Process Cartridge>

FIG. 9 is a schematic sectional view of a process cartridge forelectrophotography including an electroconductive member according to anaspect of the present disclosure as a charging roller. This processcartridge has a developing device and a charging device integrated witheach other, and is configured to be detachably attachable to a main bodyof the electrophotographic apparatus. The developing device is a devicehaving at least a developing roller 93 and a toner container 96integrated with each other, and may include a toner supply roller 94, atoner 99, a developing blade 98, and a stirring blade 910, as necessary.The charging device is a device having at least a photosensitive drum91, a cleaning blade 95, and a charging roller 92 integrated with eachother, and may include a waste toner container 97. A voltage is appliedto each of the charging roller 92, the developing roller 93, the tonersupply roller 94, and the developing blade 98.

<Electrophotographic Apparatus>

FIG. 10 is a schematic configuration diagram of an electrophotographicapparatus using the electroconductive member according to an aspect ofthe present disclosure as a charging roller. This electrophotographicapparatus is a color electrophotographic apparatus in which four processcartridges are mounted to be detachably attachable. Toners of black,magenta, yellow, and cyan are used for each process cartridge. Aphotosensitive drum 101 rotates in the direction of an arrow and isuniformly charged by a charging roller 102 to which a voltage is appliedfrom a charging bias power source, and an electrostatic latent image isformed on the surface of the photosensitive drum 101 by exposure light1011. On the other hand, a toner 109 stored in a toner container 106 issupplied to a toner supply roller 104 by a stirring blade 1010 and istransported onto a developing roller 103. Then, the developing blade 108disposed in contact with the developing roller 103 uniformly coats thesurface of the developing roller 103 with the toner 109, and at the sametime, the electric charge is imparted to the toner 109 by triboelectriccharging. The electrostatic latent image is visualized as a toner imageby developing with the toner 109 transported by the developing roller103 disposed in contact with the photosensitive drum 101.

The visualized toner image on the photosensitive drum is transferred toan intermediate transfer belt 1015 which is supported and driven by atension roller 1013 and an intermediate transfer belt driving roller1014 by a primary transfer roller 1012 to which a voltage is applied bya primary transfer bias power source. The toner images of the respectivecolors are sequentially superimposed to form a color image on theintermediate transfer belt.

A transfer material 1019 is fed into the apparatus by a paper feedroller and is transported between the intermediate transfer belt 1015and a secondary transfer roller 1016. A voltage is applied to thesecondary transfer roller 1016 from a secondary transfer bias powersource, and the color image on the intermediate transfer belt 1015 istransferred to the transfer material 1019. The transfer material 1019 towhich the color image has been transferred is fixed by a fixing device1018, and is discharged outside the apparatus to complete a printingoperation.

On the other hand, the toner remaining on the photosensitive drumwithout being transferred is scraped off by the cleaning blade 105 andstored in the waste toner storage container 107, and the cleanedphotosensitive drum 101 repeats the above steps. Further, the tonerremaining on the primary transfer belt without being transferred is alsoscraped off by the cleaning device 1017.

According to one aspect of the present disclosure, it is possible toobtain an electroconductive member that can be used as a chargingmember, a developing member, or a transfer member that can stably chargea body to be charged even when applied to a high-speedelectrophotographic image forming process. According to another aspectof the present disclosure, it is possible to obtain a process cartridgethat contributes to the formation of a high-quality electrophotographicimage. Further, according to still another aspect of the presentdisclosure, it is possible to obtain an electrophotographic imageforming apparatus capable of forming a high-quality electrophotographicimage.

EXAMPLES Example 1

(1. Manufacture of Unvulcanized Rubber Mixture for Forming Domain (CMB))

[1-1. Preparation of Unvulcanized Rubber Mixture]

The materials indicated in Table 1 were mixed in the blending amountsindicated in Table 1 using a 6-liter pressure kneader (product name:TD6-15MDX, available from Toshin) to obtain CMB. The mixing conditionswere a filling rate of 70 vol %, a blade rotation speed of 30 rpm, and20 minutes of time duration.

TABLE 1 Blending amount (parts by Raw material name mass) Raw materialStyrene butadiene rubber 100 rubber (Product name: TUFDENE 1000,available from Asahi Kasei Corporation) Electronic Carbon black 80electroconductive (Product name: TOKABLACK #5500, agent available fromTokai Carbon Co., Ltd.) Vulcanization Zinc oxide 5 acceleration aid(Product name: Zinc oxide, available from Sakai Chemical Industry Co.,Ltd.) Processing aid Zinc stearate 2 (Product name: SZ-2000, availablefrom Sakai Chemical Industry Co., Ltd.)

[1-2. Preparation of Rubber Mixture for Forming Matrix (MRC)]

The materials indicated in Table 2 were mixed in the blending amountsindicated in Table 2 using a 6-liter pressure kneader (product name:TD6-15MDX, available from Toshin) to obtain MRC. The mixing conditionswere a filling rate of 70 vol %, a blade rotation speed of 30 rpm, and16 minutes of time duration.

TABLE 2 Blending amount (parts by Raw material name mass) Raw materialButyl rubber 100 rubber (Product name: JSR Butyl 065, available fromJSR) Filler Calcium carbonate 70 (Product name: NANOX #30, availablefrom Maruo Calcium Co., Ltd.) Vulcanization Zinc oxide 7 acceleration(Product name: Zinc oxide, available aid from Sakai Chemical IndustryCo., Ltd.) Processing Zinc stearate 2.8 aid (Product name: SZ-2000,available from Sakai Chemical Industry Co., Ltd.)

[1-3. Preparation of Unvulcanized Rubber Mixture for FormingElectroconductive Layer]

The CMB and MRC obtained above were mixed in the blending amountsindicated in Table 3 using a 6-liter pressure kneader (product name:TD6-15MDX, available from Toshin). The mixing conditions were a fillingrate of 70 vol %, a blade rotation speed of 30 rpm, and 16 minutes oftime duration.

TABLE 3 Blending amount (parts by Raw material name mass) Raw materialrubber Unvulcanized domain composition 25 Raw material rubberUnvulcanized matrix composition 75

Next, a vulcanizing agent and a vulcanization accelerator indicated inTable 4 were added in the blending amount indicated in Table 4 withrespect to 100 parts by mass of the mixture of CMB and MRC, and themixture was mixed by using an open roll having a roll diameter of 12inches (0.30 m) to prepare a rubber mixture for forming anelectroconductive layer. The mixing conditions were such that by settinga rotation speed of a front roll to be 10 rpm and a rotation speed of arear roll to be 8 rpm, and a roll gap to be 2 mm, the left and rightsides were turned 20 times in total, and then by setting the roll gap tobe 0.5 mm, thinning was performed 10 times.

TABLE 4 Blending amount (parts by Raw material name mass) VulcanizingSulfur 3 agent (Product name: SULFAX PMC, available from TsurumiChemical Industry Co., Ltd.) Vulcanization Tetrabenzyl thiuram disulfide1 aid (Product name: TBZTD, available from Sanshin Chemical Co., Ltd.)

(2. Manufacture of Electroconductive Member)

[2-1. Preparation of Support Having Electroconductive Outer Surface]

As a support having an electroconductive outer surface, a round barhaving a total length of 252 mm and an outer diameter of 6 mm wasprepared by subjecting a surface of stainless steel (SUS) to electrolessnickel plating.

[2-2. Molding of Electroconductive Layer]

A die with an inner diameter of 12.5 mm was attached to a tip of acrosshead extruder that has a supply mechanism of a support and adischarge mechanism of an unvulcanized rubber roller, the temperaturesof the extruder and crosshead were set to 80° C., and a transport speedof the support was adjusted to 60 mm/sec. Under this condition, therubber mixture for forming an electroconductive layer was supplied fromthe extruder, and an outer peripheral portion of the support was coveredwith the rubber mixture for forming an electroconductive layer in thecrosshead to obtain an unvulcanized rubber roller.

Next, the unvulcanized rubber roller was put into a hot air vulcanizingfurnace at 160° C., and the rubber mixture for forming anelectroconductive layer was vulcanized by heating for 60 minutes toobtain a roller on which an electroconductive layer is formed on theouter peripheral portion of the support. After that, both ends of theelectroconductive layer were cut off by 10 mm to set a length of anelectroconductive layer portion in the longitudinal direction to be 231mm.

Finally, the surface of the electroconductive layer was polished with arotary grindstone. As a result, an electroconductive roller A1 having acrown shape with a diameter of 8.44 mm at a position of 90 mm from thecentral portion to both end sides and a central portion diameter of 8.5mm was obtained.

(3. Characteristic Evaluation)

[3-1] Checking of Matrix-Domain Structure

Whether or not the matrix-domain structure was formed in theelectroconductive layer was checked by the following method.

Using a razor, a slice was cut out so as to observe a cross sectionperpendicular to the longitudinal direction of the electroconductivelayer of the electroconductive member. Next, a cross-sectional image wasobtained by performing platinum vapor deposition, and taking aphotograph at a magnification of 1,000 using a scanning electronmicroscope (SEM) (product name: S-4800, available from HitachiHigh-Technologies Corporation).

The matrix-domain structure observed in the slice from theelectroconductive layer indicates an aspect that in the cross-sectionalimage, domains are dispersed in the matrix as illustrated in FIG. 6, andthe domains exist in an independent state without being connected toeach other. On the other hand, the domain group in which the matrix isin a state of communicating with the image was checked.

Furthermore, in order to quantify the obtained photographed image, imageprocessing software (product name: ImageProPlus, available from MediaCybernetics, Inc.) was used for the fracture surface image obtained byobservation with SEM to perform 8-bit grayscale conversion, therebyobtaining a 256-tone monochrome image. Next, the black and white of theimage was inverted so that the domain in the fracture surface becamewhite, and a binarized image was obtained. By using a counting functionfor the binarized image, the number percent K of isolated domains thatwere not connected to each other as described above was calculated withrespect to the total number of domains existing in the region of 50 μmsquare and having no contact with the frame line of the binarized image.

In a case where an arithmetic average value K (% by number) is more than80 when an electroconductive layer of an electroconductive roller A1(length in the longitudinal direction: 231 mm) is equally divided intofive regions in the longitudinal direction, equally divided into fourregions in the circumferential direction to manufacture a sliceoptionally from each region, 20 sections in total, and then the abovemeasurement is performed on the sections, the matrix-domain structure isevaluated as “Presence”, and a case where the arithmetic average value K(% by number) is less than 80, it is evaluated as “Absence”, and Table6-1 and Table 6-2 indicate the results of “presence or absence ofsea-island structure”.

[3-2] Measurement of slope from 1.0×10⁵ Hz to 1.0×10⁶ Hz and impedancefrom 1×10⁻² Hz to 1×10¹ Hz

The following measurements were performed to evaluate the slope of theimpedance from 1.0×10⁵ to 1.0×10⁶ Hz and the impedance from 1.0×10⁻² Hzto 1.0×10¹ Hz, in the electroconductive member.

First, as a pretreatment, vacuum platinum vapor deposition was performedon the electroconductive roller A1 while rotating to form a measurementelectrode. At this time, a masking tape was used to form a strip-shapedelectrode having a width of 1.5 cm in the longitudinal direction anduniform in the circumferential direction. By forming the electrode, theinfluence of the contact resistance between the measurement electrodeand the electroconductive member can be eliminated as much as possibledue to the surface roughness of the electroconductive member. Next, analuminum sheet was wound around the electrode without any gap to form ameasurement electrode on the electroconductive member side.

FIG. 11 illustrates a schematic diagram of a state where a measurementelectrode is formed on an electroconductive roller. In FIG. 11, 111 isan electroconductive support, 112 is an electroconductive layer having amatrix-domain structure, 113 is a platinum vapor deposition layer, and114 is an aluminum sheet.

FIG. 12 illustrates a sectional view of a state where the measurementelectrode is formed on an electroconductive member. 121 is anelectroconductive support, 122 is an electroconductive layer having amatrix-domain structure, 123 is a platinum vapor deposition layer, and124 is an aluminum sheet. As illustrated in FIG. 12, it is importantthat the electroconductive support and the measurement electrodesandwich the electroconductive layer having a matrix-domain structure.

Then, the aluminum sheet was connected to the measurement electrode onthe side of the impedance measuring device (Solartron 1260 and Solartron1296, available from Solartron). FIG. 13 illustrates a schematic diagramof this measurement system. Impedance measurement was performed by usingan electroconductive support and an aluminum sheet as two electrodes formeasurement.

When measuring the impedance, the electroconductive roller A1 was leftin an environment of a temperature of 23° C. and a humidity of 50% RHfor 48 hours to saturate the water content of the electroconductivemember A1.

Impedance measurement was performed at a temperature of 23° C. and ahumidity of 50% RH at an AC voltage with an amplitude of 1 Vpp and afrequency of from 1.0×10⁻² Hz to 1.0×10⁷ Hz (when the frequency changesby one digit, five points each are measured) to obtain the absolutevalue of impedance. Then, the measurement result was plotted inlogarithmic log of the absolute value of the impedance and the frequencyusing a spreadsheet software such as Excel (registered trademark). Fromthe graph obtained by the logarithmic log plot, the arithmetic averagevalue of each of (a) the slope from 1.0×10⁵ Hz to 1.0×10⁶ Hz and (b) theabsolute value of impedance from 1.0×10⁻² Hz to 1.0×10¹ Hz wascalculated. Regarding the measurement position, the electroconductivelayer of the electroconductive roller A1 (length in the longitudinaldirection: 230 mm) was equally divided into five regions in thelongitudinal direction to form a measurement electrode optionally fromeach region, five measurement electrodes in total, and then the abovemeasurement and calculation of the arithmetic average value wereperformed. The evaluation results are indicated in Table 6-1 and Table6-2 as the results of “(a) slope” and “(b) impedance” of theelectroconductive layer.

[3-3] Measurement of Impedance from 1.0×10⁻² Hz to 1.0×10¹ Hz forElectroconductive Support

The impedance measurement from 1.0×10⁻² Hz to 1.0×10¹ Hz was performedin the same manner as in [3-3] on the electroconductive support of theelectroconductive roller A1 with the electroconductive layer peeled off.The evaluation results are indicated in Table 6-1 and Table 6-2 as“impedance” of the electroconductive support.

[3-4] Measurement of Volume Resistivity of Matrix

The following measurements were performed to evaluate the volumeresistivity of the matrix contained in the electroconductive layer. Ascanning probe microscope (SPM) (product name: Q-Scope250, availablefrom Quesant Instrument Corporation) was operated in contact mode.First, from the electroconductive elastic layer of the electroconductiveroller A1, a microtome (product name: Leica EM FCS, available from LeicaMicrosystems) was cut out as an ultrathin slice with a thickness of 1 μmat a cutting temperature of −100° C. When the ultrathin slices were cutout, the direction of the cross section perpendicular to thelongitudinal direction of the electroconductive member was set inconsideration of the direction in which electric charges are transportedfor discharge.

Next, in an environment with a temperature of 23° C. and a humidity of50% RH, the ultrathin slice was placed on a metal plate, a part that isin direct contact with the metal plate was selected, and a partcorresponding to the matrix was brought into contact with a SPMcantilever, a voltage of 50 V was applied to the cantilever for fiveseconds, the current value was measured, and the arithmetic averagevalue for five seconds was calculated.

The surface shape of the measurement slice was observed with the SPM,and the thickness of the measurement location was calculated from theobtained height profile. Further, a recess area of the contact portionof the cantilever was calculated from the observation result of thesurface shape. The volume resistivity was calculated from the thicknessand the recess area to obtain the volume resistivity of the matrix.

The electroconductive layer of the electroconductive roller A1(longitudinal direction length: 230 mm) was equally divided into fiveregions in the longitudinal direction, equally divided into four regionsin the circumferential direction to manufacture a slice optionally fromeach region, 20 slices in total, and then the above measurement wasperformed on the sections. The average value was used as the volumeresistivity of the matrix. The evaluation results are indicated in Table6-1 and Table 6-2 as “volume resistivity” of the matrix.

[3-5] Measurement of Volume Resistivity of Domain

In order to evaluate the volume resistivity of the domain contained inthe electroconductive layer, the volume resistivity of the domain wasmeasured by the same method except that in the measurement of the volumeresistivity of the above matrix, the measurement is performed at alocation corresponding to the domain of the ultrathin slice, and thevoltage for measurement was set to be 1 V. The evaluation results areindicated in Table 6-1 and Table 6-2 as “volume resistivity” of thedomain.

[3-6] Evaluation of Domain Shape

The shape of the domain contained in the electroconductive layer wasevaluated by a method of quantifying an observation image obtained bythe following scanning electron microscope (SEM) by image processing.

A thin piece having a thickness of 1 mm was cut out by the same methodas in [3-4] Measurement of the volume resistivity of the matrix. At thistime, the thin piece acquired a plane perpendicular to the axis of theelectroconductive support and a fracture surface of a cross sectionparallel to the plane. The cut-out positions from the electroconductivelayer were set as three positions of, when the length of theelectroconductive layer in the longitudinal direction is defined as L,the center in the longitudinal direction, and L/4 from both ends of theelectroconductive layer toward the center. Platinum was vapor-depositedon the slice to obtain a vapor-deposited slice. Next, an observationimage was obtained by taking a photograph of the surface of thevapor-deposited slice at a magnification of 1,000 using a scanningelectron microscope (SEM) (product name: S-4800, available from HitachiHigh-Technologies Corporation).

Next, when the thickness of the electroconductive layer is defined as T,a 15 μm square region at any three locations, for each of the threeslices obtained from the three measurement positions, nine locations intotal, in the thickness region from the outer surface of theelectroconductive layer to the depth of from 0.1 T to 0.9 T wasextracted as an analysis image.

Next, in order to quantify the shape of the domain in the analysisimage, image processing software “ImageProPlus” (product name, availablefrom Media Cybernetics, Inc.) was used to perform 8-bit grayscaleconversion, thereby obtaining a 256-tone monochrome image. Next, theblack and white of the image was inverted so that the domain in thefracture surface became white, and a binarized image was obtained. Next,the following items were calculated for the domain group existing in thebinarized image by the counting function for the binarized image.

Perimeter A (μm)

Envelope perimeter B (μm)

By substituting these values into the following Equation (5), the ratioof the number of domains satisfying the condition of Equation (5) wascalculated as the number % with respect to the total number of domaingroups in each evaluation image, and further, the average value of thenine evaluation images was calculated and used as an index of the domainshape. The results are indicated in Table 6-1 and Table 6-2. In Tables6-1 and 6-2, the value obtained by substituting in Equation (5) is the“perimeter ratio A/B”, and the proportion of domains that satisfy theEquation (5) is indicated as the “shape index”.

1.00≤AB≤1.10  Equation (5)

(A: Perimeter of Domain, B: Envelope Perimeter of Domain)

[3-7] Cross-sectional area ratio of electronic electroconductivematerial in domain, the cross-sectional area ratio of the electronicelectroconductive material in the domain, which is correlated with theirregular shape of the circumferential surface of the domain measuredfor the uniformity of the volume resistivity of the domain, andvariation of a cross-sectional area ratio of the electronicelectroconductive material in the domain, which is correlated with theuniformity of the volume resistivity of the domain, were measured.

A thin piece for observation was cut out by the same method as themeasurement of the domain shape in [3-6] so as to obtain an observationimage by taking a photograph of the fracture surface at a magnificationof 5,000 using a scanning electron microscope (SEM) (product name:S-4800, available from Hitachi High-Technologies Corporation). Then, theimage processing software “ImageProPlus” (product name, available fromMedia Cybernetics, Inc.) was used to binarize the observation image sothat the carbon black particles can be distinguished, and by using thecounting function, the cross-sectional area S of the domain in theanalysis image and the total Sc of the cross-sectional areas of thecarbon black particles as the electronic electroconductive agentcontained in the domain were calculated. Then, σr/μr was calculated fromthe arithmetic average value μr of Sc/S as the cross-sectional arearatio of the electronic electroconductive material in the domain, μr andthe standard deviation σr of μr as an index of the uniformity of thevolume resistivity of the domain.

In the calculation of μr and σr, when the thickness of theelectroconductive layer is defined as T, a 15 μm square region at anythree locations, for each of the three slices obtained from the threemeasurement positions, nine locations in total, in the thickness regionfrom the outer surface of the electroconductive layer to the depth offrom 0.1 T to 0.9 T was extracted as an analysis image. The measurementwas performed in the extracted regions, and the arithmetic average valueobtained from the nine regions was calculated. The evaluation resultsare indicated in Table 6-1 and Table 6-2 as “electronicelectroconductive material cross-sectional area ratio μr of domain” and“domain volume resistivity uniformity σr/μr”.

[3-8] Measurement of Domain Size

The measurement of domain size was performed in such a manner that theobservation image at a magnification of 5,000 obtained by themeasurement of the uniformity of volume resistivity of the domain in[3-7] described above was binarized by the image processing software“ImageProPlus” (product name, available from Media Cybernetics), andquantified by the counting function so as to calculate thecross-sectional area S of the domain group. Next, an equivalent circlediameter D was calculated from the cross-sectional area S of eachdomain. Specifically, D=(S/2πr)^(0.5) was calculated using the area S ofthe domain.

In the domain size measurement, when the thickness of theelectroconductive layer is defined as T, a 50 μm square region at anythree locations, for each of the three slices obtained from the threemeasurement positions, nine locations in total, in the thickness regionfrom the outer surface of the electroconductive layer to the depth offrom 0.1 T to 0.9 T was extracted as an analysis image. The measurementwas performed in the extracted regions, and the arithmetic average valuefrom the nine regions was calculated. The results are indicated in Table6-1 and Table 6-2 as “Equivalent circle diameter D”.

[3-9] Measurement of Particle Size Distribution of the Domain

The particle size distribution of the domain was measured as follows toevaluate the uniformity of the domain size. First, a binarized image wasobtained using the image processing software “ImageProPlus” (productname, available from Media Cybernetics) on the observation image at amagnification of 5,000 obtained by the [3-8] measurement of domain sizewith a scanning electron microscope (product name: S-4800, availablefrom Hitachi High-Technologies Corporation). Next, for the binarizedimage, the average value D and the standard deviation ad were calculatedfor the domain group in the binarized image, and then σd/D, which is anindex of the particle size distribution, was calculated.

In the measurement of σd/D particle size distribution of the domainsize, when the thickness of the electroconductive layer is defined as T,a 50 μm square region at any three locations, for each of the threeslices obtained from the three measurement positions, nine locations intotal, in the thickness region from the outer surface of theelectroconductive layer to the depth of from 0.1 T to 0.9 T wasextracted as an analysis image to calculate an arithmetic average valueat nine locations. The evaluation results are indicated in Table 6-1 andTable 6-2 as “particle size distribution ad/D” of the domain.

[3-10] Measurement of Inter-Domain Surface Distances

The following measurements were performed to evaluate the inter-domainsurface distances.

The distance between the domains is, first, a binarized image wasobtained using the image processing software LUZEX (available fromNireco Corporation) on the observation image at a magnification of 5,000obtained by the [3-8] measurement of domain size with a scanningelectron microscope (product name: S-4800, available from HitachiHigh-Technologies Corporation). Then, for the binarized image, thedistribution of the distances between the wall surfaces of the domainwas calculated, and then the arithmetic average value of thedistribution was calculated.

In the measurement of inter-domain surface distances, when the thicknessof the electroconductive layer is defined as T, a 50 μm square region atany three locations, for each of the three slices obtained from thethree measurement positions, nine locations in total, in the thicknessregion from the outer surface of the electroconductive layer to thedepth of from 0.1 T to 0.9 T was extracted as an analysis image tocalculate an arithmetic average value at nine locations. The evaluationresults are indicated in Table 6-1 and Table 6-2 as the “inter-domainsurface distances” of the matrix.

[3-11] Measurement of Uniformity of Inter-Domain Surface Distances

The uniformity of the inter-domain surface distances was performed asfollows. First, a binarized image was obtained using the imageprocessing software LUZEX (available from Nireco Corporation) on theobservation image at a magnification of 5,000 obtained by the [3-9]measurement of domain size with a scanning electron microscope (productname: S-4800, available from Hitachi High-Technologies Corporation).Next, for the binarized image, the arithmetic average value Dm and thestandard deviation am were calculated from the distribution of thedistance between the wall surfaces of the domains, and then am/Dm, whichis an index of the uniformity of the distance between the domains, wascalculated.

In the measurement of am/Dm, which is an index of the uniformity of thedistance between the domains, when the thickness of theelectroconductive layer is defined as T, a 50 μm square region at anythree locations, for each of the three slices obtained from the threemeasurement positions, nine locations in total, in the thickness regionfrom the outer surface of the electroconductive layer to the depth offrom 0.1 T to 0.9 T was extracted as an analysis image to calculate anarithmetic average value at nine locations. The evaluation results areindicated in Table 6-1 and Table 6-2 as “uniformity of inter-domainsurface distances am/Dm” of the matrix.

[3-12] Measurement of Volume Fraction

The volume fraction of the domain was calculated by measuring theelectroconductive layer in three dimensions using FIB-SEM.

Specifically, a slice image group was obtained by repeatingcross-section exposure by a focused ion beam and SEM observation byusing FIB-SEM (available from FEI) (details described above).

The obtained image was three-dimensionally constructed in amatrix-domain structure using 3D visualization/analysis software Avizo(available from FEI). Next, the analysis software discriminated thematrix-domain structure by binarization.

Furthermore, in order to quantify the volume fraction, the volume of thedomain contained in any sample of cubic shape with a side of 10 μm inthe three-dimensional image was calculated.

In the measurement of the volume fraction of the domain, when thethickness of the electroconductive layer is defined as T, a cubic shapewith a side of 10 μm at any three locations, for each of the threeslices obtained from the three measurement positions, nine locations intotal, in the thickness region from the outer surface of theelectroconductive layer to the depth of from 0.1 T to 0.9 T wasextracted as a sample to calculate an arithmetic average value at ninelocations. The evaluation results are indicated in Table 6-1 and Table6-2 as “domain volume fraction”.

(4. Image Evaluation)

[4-1] Evaluation of Charging Ability

The following evaluations were performed in order to check the functionof suppressing discharge omission of the electroconductive roller A1.First, as an electrophotographic apparatus, an electrophotographic laserprinter (product name: Laserjet M608dn, available from HP) was prepared.Next, the electroconductive roller A1, the electrophotographicapparatus, and the process cartridge were left in an environment of 23°C. and 50% RH for 48 hours for the purpose of adjusting to themeasurement environment.

In order to evaluate in a high-speed process, the laser printer wasmodified so that the number of output sheets per unit time was 75sheets/minute with A4 size paper, which was larger than the number oforiginal output sheets. At that time, the output speed of the recordingmedium was 370 mm/sec and the image resolution was 1,200 dpi. Further,the pre-exposure device in the laser printer was removed.

Further, the process cartridge was modified and a surface potentialprobe (main body: Model 347, Trek Corp. probe: Model 3800S-2) wasinstalled so as to measure the drum surface potential after the chargingprocess.

The electroconductive roller A1 left in the above environment was set asa charging roller of the process cartridge and incorporated into a laserprinter.

Under the same environment as above, by an external power supply(Trek615 available from Trek Japan), a voltage of −1000 V was applied tothe electroconductive roller A1 to measure the surface potential of thephotosensitive drum when outputting a solid white image and a solidblack image. Then, a difference in surface potential of thephotosensitive drum after the charging process when the solid blackimage was output and when the solid white image was output wascalculated as the charging ability of the electroconductive roller A1.The evaluation results are indicated in Table 6-1 and Table 6-2 as“black and white potential difference”.

[4-2] Ghost Image Evaluation

The effect of forming a uniform discharge against the unevenness of thesurface potential of the photosensitive drum before charging in thehigh-speed process of the electroconductive roller A1 was checked by thefollowing method.

The laser printer used in the above “Evaluation of charging ability” wasused to form an evaluation image. Similar to the above “Evaluation ofcharging ability”, the electroconductive roller A1, the laser printer,and the process cartridge are left in the environment of 23° C. 50% RHfor 48 hours for the purpose of adjusting to the measurementenvironment, so that an evaluation image was formed under the sameenvironment.

The evaluation image had an “E” letter at the top of the image and ahalftone image from the center to the bottom of the image.

Specifically, the top 10 cm of the image was an image in which theletter “E” in the alphabet of 4 points in size was printed so that thecoverage was 4% with respect to the area of A4 size paper. As a result,after the transfer process, that is, before the charging process, thesurface potential of the photosensitive drum can be uneven in the regionof about one round of the photosensitive drum along the surfacepotential corresponding to the first letter “E”. FIG. 14 illustrates anexplanatory diagram of the evaluation image.

Furthermore, a halftone image (an image in which a horizontal linehaving a width of one dot and a distance of two dots is drawn in thedirection perpendicular to the rotation direction of the photosensitivedrum) was output from the lower part of 10 cm. This halftone image wasvisually observed and evaluated according to the following criteria. Theresults are indicated in Table 6-1 and Table 6-2.

[Evaluation of “E” Letter on Halftone Image]

Rank A: No image unevenness derived from the letter “E” is observed onthe halftone image even when observed with a microscope.Rank B: Although there is no image unevenness derived from the letter“E” on a part of the halftone image by visual observation, imageunevenness derived from the letter “E” is observed with a microscope.Rank C: An image of the letter “E” is visually observed on part on thehalftone image.Rank D: An image of the letter “E” is visually observed on the entiresurface of the halftone image.

Example 2 to Example 38

Electroconductive members A2 to A38 are manufactured in the same manneras in Example 1 except that the materials and conditions indicated inTables 5A-1 to 5A-4 are used for the raw rubber, the electroconductiveagent, the vulcanizing agent, and the vulcanization accelerator.

For details of the materials indicated in Tables 5A-1 to 5A-4, therubber material is indicated in Table 5B-1, the electroconductive agentis indicated in Table 5B-2, and the vulcanizing agent and acceleratorare indicated in Table 5B-3.

Further, in Example 36, using a compound available from Toho Tenax(product name: rPEEK CF30), it is possible to mold into a round bar typewhich can be molded in the same shape as the support in Example 1 at amold temperature of 380° C. A round bar made of the obtainedelectroconductive resin (total length 252 mm, outer diameter 6 mm) wasused as a support.

In Example 37, the following adhesive (metalloc (metalloc N-33,available from Toyo Kagaku Kenkyusho Co., Ltd., diluted with methylisobutyl ketone at 25% by weight) was applied by a roll coater over theentire circumference in the range of 230 mm including the centralportion excluding the both ends 11 mm in the longitudinal direction ofthe outer peripheral surface of the round bar made of theelectroconductive resin molded in the same manner as in Example 36.After application, the adhesive was baked by heating at 180° C. for 30minutes. In Example 37, the round bar with a primer layer thus obtainedwas used as a support.

In Example 38, 35% by weight of a phenol resin (product name: PR-50716available from Sumitomo Bakelite Co., Ltd.) and 5% by weight ofhexamethylenetetramine (product name: urotropine available from SumitomoSeika Chemical Co., Ltd.) were heated for 3 minutes with a heating rollat 90° C., and after melt-kneading, the mixture was taken out, crushed,and the molding material crushed into granules was injection-molded at amold temperature of 175° C. to mold a round bar. The whole outer surfaceof the obtained round bar made of an insulating resin was subjected toplatinum vapor deposition and used as a support.

For each charging member obtained in Examples 2 to 38, the same items asin Example 1 were measured and evaluated. The obtained results areindicated in Table 6-1 and Table 6-2.

The logarithmic log plot obtained in Example 22 is illustrated in FIG.15.

TABLE 5A-1 Unvulcanized domain rubber composition ElectroconductiveElectroconductive agent support Raw material rubber type PartsDispersion Electroconductive SP Mooney by time Mooney Type surfaceMaterial abbreviation value viscosity Type mass DBP min viscosityExample 1 SUS Ni plating SBR T1000 16.8 45 #5500 80 155 30 84 Example 2SUS Ni plating SBR T1000 16.8 45 #7360 100  87 30 85 Example 3 SUS Niplating SBR T1000 16.8 45 #5500 80 155 30 82 Example 4 SUS Ni platingSBR T1000 16.8 45 #5500 80 155 30 83 Example 5 SUS Ni plating SBR T100016.8 45 #5500 80 155 30 85 Example 6 SUS Ni plating SBR T1000 16.8 45#5500 80 155 30 84 Example 7 SUS Ni plating BR T0700 17.1 43 #5500 100155 30 89 Example 8 SUS Ni plating BR T0700 17.1 43 #5500 100 155 30 90Example 9 SUS Ni plating BR T0700 17.1 43 #5500 100 155 30 89 Example 10SUS Ni plating BR T0700 17.1 43 #5500 80 155 30 86 Example 11 SUS Niplating BR T0700 17.1 43 #5500 60 155 30 71 Example 12 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 80 155 30 74 Example 13 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 82 155 30 81 Example 14 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 85 155 30 85 Example 15 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 90 155 30 90 Example 16 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 80 155 30 77 Example 17 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 80 155 30 76 Example 18 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 60 155 30 73 Example 19 SUS Ni platingButyl JSR Butyl 065 15.8 32 #5500 40 155 30 65 Example 20 SUS Ni platingNBR N230S 20 32 #7360 60  87 30 65 Example 21 SUS Ni plating NBR N230S20 32 #7360 40  87 30 55

TABLE 5A-2 Unvulcanized matrix rubber composition UnvulcanizedUnvulcanized Electro- rubber rubber conductive composition dispersionVulcanizing Vulcanization agent Domain Matrix Rota- Knead- agentaccelerator Raw material rubber type Parts Parts Parts tion ing MaterialParts Material Parts SP Mooney by Mooney by by speed time abbrevi- byabbrevi- by Material abbreviation value viscosity Type mass viscositymass mass rpm min ation mass ation mass Example 1 Butyl JSR Butyl 06515.8 32 — — 40 15 85 30 20 Sulfur 3 TT 3 Example 2 Butyl JSR Butyl 06515.8 32 — — 40 15 85 30 20 Sulfur 3 TT 3 Example 3 Butyl JSR Butyl 06515.8 32 — — 41 20 80 30 20 Sulfur 3 TT 3 Example 4 Butyl JSR Butyl 06515.8 32 — — 38 22 78 30 20 Sulfur 3 TT 3 Example 5 Butyl JSR Butyl 06515.8 32 — — 39 25 75 30 20 Sulfur 3 TT 3 Example 6 EPDM Esplene301A 1744 — — 50 20 80 30 20 Sulfur 3 TET 1 Example 7 SBR T1000 16.8 45 — — 5420 80 30 20 Sulfur 3 TBZTD 1 Example 8 SBR T2003 17 45 — — 53 20 80 3020 Sulfur 3 TBZTD 1 Example 9 SBR A303 17 46 — — 55 20 80 30 20 Sulfur 3TBZTD 1 Example 10 EPDM Esplene301A 17 44 — — 52 20 80 30 20 Sulfur 3TET 3 Example 11 EPDM Esplene301A 17 44 — — 51 20 80 30 20 Sulfur 3 TET3 Example 12 EPDM Esplene301A 17 44 — — 51 22 78 30 20 Sulfur 3 TET 3Example 13 EPDM Esplene301A 17 44 — — 53 22 78 30 20 Sulfur 3 TET 3Example 14 EPDM Esplene301A 17 44 — — 52 22 78 30 20 Sulfur 3 TET 3Example 15 EPDM Esplene301A 17 44 — — 51 22 78 30 20 Sulfur 3 TET 3Example 16 SBR T1000 16.8 45 — — 52 22 78 30 20 Sulfur 2 TT 2 Example 17SBR A303 17 46 — — 52 22 78 30 20 Sulfur 2 TT 2 Example 18 EPDMEsplene301A 17 44 — — 50 22 78 30 20 Sulfur 3 TET 3 Example 19 EPDMEsplene301A 17 44 — — 49 22 78 30 20 Sulfur 3 TET 3 Example 20 EPDMEsplene301A 17 44 — — 52 25 75 30 20 Sulfur 3 TET 3 Example 21 EPDMEsplene301A 17 44 — — 49 25 75 30 20 Sulfur 3 TET 3

TABLE 5A-3 Unvulcanized domain rubber composition Electroconductiveagent Electroconductive support Raw material rubber type PartsDispersion Electroconductive SP Mooney by time Mooney Type surfaceMaterial abbreviation value viscosity Type mass DBP min viscosityExample 22 SUS Ni plating NBR N230S 20 32 #7360 60 87 30 66 Example 23SUS Ni plating NBR N230S 20 32 #7360 40 87 30 58 Example 24 SUS Niplating NBR N230S 20 32 #7360 60 87 30 68 Example 25 SUS Ni plating SBRT2100 17 78 #5500 80 155 30 105 Example 26 SUS Ni plating NBR DN401LL17.4 32 #5500 60 155 30 72 Example 27 SUS Ni plating SBR T2100 17 78#5500 40 155 30 95 Example 28 SUS Ni plating NBR DN401LL 17.4 32 #550040 155 30 70 Example 29 SUS Ni plating NBR N202S 20.4 57 #7360 60 87 3086 Example 30 SUS Ni plating NBR N202S 20.4 57 #7360 60 87 30 85 Example31 SUS Ni plating NBR N202S 20.4 57 #7360 40 87 30 65 Example 32 SUS Niplating NBR N202S 20.4 57 #7360 40 87 30 66 Example 33 SUS Ni platingNBR N202S 20.4 57 #7360 60 87 30 84 Example 34 SUS Ni plating NBR N202S20.4 57 #7360 60 87 10 84 Example 35 SUS Ni plating NBR N202S 20.4 57#5500 40 87 30 75 Example 36 Electroconductive — Butyl JSR Butyl 06515.8 32 #5500 80 155 30 78 resin core metal Example 37 ElectroconductivePrimer Butyl JSR Butyl 065 15.8 32 #5500 80 155 30 80 resin core metalExample 38 Insulating resin Primer Butyl JSR Butyl 065 15.8 32 #5500 80155 30 79 core metal

TABLE 5A-4 Unvulcanized matrix rubber composition UnvulcanizedUnvulcanized Electro- rubber rubber conductive composition dispersionVulcanizing Vulcanization agent Domain Matrix Number Knead- agentaccelerator Raw material rubber type Parts Parts Parts of ing MaterialParts Material Parts SP Mooney by Mooney by by rotations time abbrevi-by abbrevi- by Material abbreviation value viscosity Type mass viscositymass mass rpm min ation mass ation mass Example 22 SBR A303 17 46 — — 5125 75 30 20 Sulfur 3 TBZTD 1 Example 23 SBR A303 17 46 — — 51 25 75 3020 Sulfur 3 TBZTD 1 Example 24 EPDM Esplene301A 17 44 — — 49 25 75 30 20Sulfur 3 TET 3 Example 25 EPDM Esplene301A 17 44 — — 48 15 85 30 20Sulfur 3 TET 3 Example 26 SBR A303 17 46 — — 50 15 85 30 20 Sulfur 3TBZTD 1 Example 27 EPDM Esplene301A 17 44 — — 51 15 85 30 20 Sulfur 3TET 3 Example 28 SBR A303 17 46 — — 52 15 85 30 20 Sulfur 3 TBZTD 1Example 29 EPDM Esplene505A 16 47 — — 52 25 75 30 20 Sulfur 3 TET 3Example 30 SBR T1000 16.8 45 — — 50 25 75 30 20 Sulfur 3 TBZTD 1 Example31 EPDM Esplene505A 16 47 — — 51 25 75 30 20 Sulfur 3 TET 3 Example 32SBR T1000 16.8 45 — — 52 25 75 30 20 Sulfur 3 TBZTD 1 Example 33 SBRT1000 16.8 45 — — 51 25 75 30 10 Sulfur 3 TBZTD 1 Example 34 SBR T100016.8 45 — — 42 25 75 30 20 Sulfur 3 TBZTD 1 Example 35 SBR T1000 16.8 45— — 51 25 75 30 20 Sulfur 3 TBZTD 1 Example 36 EPDM Esplene301A 17 44 —— 50 22 78 30 20 Sulfur 3 TT 3 Example 37 EPDM Esplene301A 17 44 — — 5022 78 30 20 Sulfur 3 TT 3 Example 38 EPDM Esplene301A 17 44 — — 51 22 7830 20 Sulfur 3 TT 3

TABLE 5B-1 Rubber material Manu- facturer's Material abbreviationMaterial name Product name name Butyl Butyl065 Butyl rubber JSR Butyl065 JSR Corporation BR T0700 Polybutadiene JSR T0700 JSR rubberCorporation ECO CG103 Epichloro- EPICHLOMER Osaka soda hydrin CG103 Co.,Ltd. rubber EPDM Esplene301A Ethylene Esprene301A Sumitomo propyleneChemical diene rubber Company, Limited EPDM Esplene505A EthyleneEsprene505A Sumitomo propylene Chemical diene rubber Company, LimitedNBR DN401LL Acrylonitrile Nipol DN401LL Zeon butadiene Corporationrubber NBR N230SV Acrylonitrile NBR N230SV JSR butadiene Corporationrubber NBR N230S Acrylonitrile NBR N230S JSR butadiene Corporationrubber NBR N202S Acrylonitrile NBR N202S JSR butadiene Corporationrubber SBR T2003 Styrene TUFDENE Asahi Kasei butadiene 2003 Corporationrubber SBR T1000 Styrene TUFDENE Asahi Kasei butadiene 1000 Corporationrubber SBR T2100 Styrene TUFDENE Asahi Kasei butadiene 2100 Corporationrubber SBR A303 Styrene ASAPRENE Asahi Kasei butadiene 303 Corporationrubber

TABLE 5B-2 Electroconductive agent Material Manufacturer's abbreviationMaterial name Product name name #7360 Electroconductive TOKABLACK TokaiCarbon carbon black #7360 SB Co., Ltd. #5500 Electroconductive TOKABLACKTokai Carbon carbon black #5500 Co., Ltd. Ketjen ElectroconductiveCARBRON LION SPECIALTY carbon black ECP CHEMICALS CO., Ltd. LV IoninLV70 ADEKA electroconductive agent

TABLE 5B-3 Vulcanizing agent and a Vulcanization accelerator Materialabbreviation Material name Product name Manufacturer's name SulfurSulfur SULFAX PMC Tsurumi Chemical Industry Co., Ltd. TT TetramethylNOCCELER Ouchi Shinko thiuram TT-P Chemical disulfide Industrial Co.,Ltd TBZTD Tetrabenzyl SANCELER Sanshin Chemical thiuram TBZTD Industrydisulfide Co., Ltd. TET Tetraethyl SANCELER Sanshin Chemical thiuramTET-G Industry disulfide Co., Ltd.

TABLE 6-1 Evaluation of characteristics of matrix domain configurationMatrix Uniformity Impedance characteristics of inter- DomainElectroconductive Electro- Inter- domain Volume Presence layerconductive domain surface resistivity of sea- (a) (b) support Volumesurface distances Volume uniformity island Slope Impedance Impedanceresistivity distances σm/Dm resistivity σr/μr structure a. u. Ω Ω Ωcm μm— Ωcm — Example 1 Presence −0.32 1.52E+03 9.08E−03 7.13E+16 0.21 0.252.59E+01 0.15 Example 2 Presence −0.33 1.08E+03 5.95E−03 5.22E+16 0.250.22 1.15E+01 0.12 Example 3 Presence −0.33 1.55E+03 3.32E−03 3.04E+160.45 0.21 2.73E+01 0.13 Example 4 Presence −0.38 2.54E+03 8.27E−038.16E+16 0.85 0.23 8.69E+01 0.15 Example 5 Presence −0.42 3.87E+036.80E−03 6.62E+16 1.15 0.25 7.62E+00 0.18 Example 6 Presence −0.351.54E+03 7.98E−03 9.58E+15 0.23 0.22 4.43E+01 0.12 Example 7 Presence−0.32 4.01E+03 7.99E−03 1.47E+14 0.24 0.24 2.56E+01 0.18 Example 8Presence −0.31 6.58E+03 3.88E−03 4.69E+13 0.22 0.21 7.69E+01 0.20Example 9 Presence −0.3  1.98E+04 4.24E−03 9.02E+12 0.21 0.20 6.91E+010.18 Example 10 Presence −0.38 3.32E+04 3.66E−03 7.97E+15 0.25 0.259.61E+01 0.11 Example 11 Presence −0.42 1.02E+05 6.52E−03 2.21E+15 0.230.25 7.93E+03 0.13 Example 12 Presence −0.36 2.39E+03 9.23E−03 8.39E+140.23 0.23 1.27E+01 0.15 Example 13 Presence −0.36 9.73E+03 3.57E−031.64E+14 0.55 0.21 5.88E+01 0.18 Example 14 Presence −0.41 1.26E+045.48E−03 8.21E+15 0.91 0.22 1.38E+01 0.12 Example 15 Presence −0.526.13E+04 1.42E−04 6.42E+15 1.92 0.23 5.02E+00 0.13 Example 16 Presence−0.55 9.05E+03 5.15E−04 3.22E+14 0.24 0.24 2.55E+01 0.14 Example 17Presence −0.62 1.27E+04 3.66E−04 2.11E+12 0.45 0.26 3.22E+01 0.14Example 18 Presence −0.51 7.63E+04 9.33E−03 2.54E+15 0.22 0.24 1.18E+010.14 Example 19 Presence −0.5  9.96E+05 1.97E−03 6.40E+15 0.21 0.204.19E+03 0.15 Example 20 Presence −0.54 7.82E+05 6.37E−03 9.86E+15 0.230.21 5.94E+01 0.11 Example 21 Presence −0.68 7.64E+05 9.96E−03 5.00E+150.24 0.21 9.41E+03 0.13 Evaluation of characteristics of matrix domainconfiguration Domain Electronic electro- conductive material Imageevaluation Equivalent Particle cross- Black and circle size sectionalPerimeter Shape Domain white diameter distribution area ratio indexvolume potential Ghost D σd/D ratio μr A/B Number fraction differenceimage μm — % — % % V — Example 1 0.22 0.26 26.8 1.09 82 14.0 1 A Example2 0.23 0.24 28.0 1.04 89 13.6 1 A Example 3 0.44 0.22 26.2 1.04 89 18.92 A Example 4 0.51 0.23 27.0 1.07 88 20.6 10 A Example 5 0.81 0.21 26.21.07 84 23.4 15 A Example 6 0.23 0.24 26.1 1.04 81 18.2 2 A Example 70.21 0.21 27.4 1.06 80 18.8 3 A Example 8 0.21 0.22 27.9 1.01 82 18.6 10A Example 9 0.25 0.20 27.2 1.08 85 18.5 15 A Example 10 0.25 0.20 26.21.06 94 18.8 20 A Example 11 0.24 0.20 25.7 1.06 82 19.1 24 A Example 121.11 0.24 26.1 1.03 83 20.8 7 A Example 13 1.33 0.23 26.1 1.09 84 20.713 A Example 14 1.52 0.21 26.3 1.03 90 20.6 20 A Example 15 1.66 0.1926.3 1.02 84 20.4 23 A Example 16 1.55 0.20 26.6 1.07 89 20.9 10 AExample 17 1.99 0.23 26.4 1.07 84 21.1 15 A Example 18 2.55 0.20 25.91.09 85 20.2 30 B Example 19 2.38 0.25 24.6 1.10 91 20.4 35 B Example 204.8  0.26 26.5 1.08 90 22.8 28 B Example 21 4.9  0.23 24.1 1.04 84 23.136 B

TABLE 6-2 Evaluation of characteristics of matrix domain configurationMatrix Uniformity Impedance characteristics of inter- DomainElectroconductive Electro- Inter- domain Volume Presence layerconductive domain surface resistivity of sea- (a) (b) support Volumesurface distances Volume uniformity island Slope Impedance Impedanceresistivity distances σm/Dm resistivity σr/μr structure a. u. Ω Ω Ωcm μm— Ωcm — Example 22 Presence −0.63 8.78E+04 3.17E−03 5.92E+12 0.26 0.226.99E+01 0.17 Example 23 Presence −0.72 2.19E+06 9.54E−03 9.80E+12 0.230.23 8.93E+03 0.11 Example 24 Presence −0.79 9.45E+04 1.71E−03 8.08E+150.21 0.23 7.03E+01 0.15 Example 25 Presence −0.48 2.28E+04 4.50E−032.95E+15 2.9 0.26 1.03E+01 0.14 Example 26 Presence −0.68 2.13E+055.29E−04 2.55E+12 3.2 0.24 6.55E+03 0.20 Example 27 Presence −0.665.27E+05 3.33E−04 3.55E+15 3.1 0.24 9.11E+03 0.15 Example 28 Presence−0.58 2.00E+05 9.26E−03 6.19E+12 3.1 0.22 9.36E+03 0.13 Example 29Presence −0.71 9.60E+04 6.96E−03 6.27E+15 5.6 0.20 5.76E+01 0.15 Example30 Presence −0.75 9.08E+04 5.69E−03 5.55E+12 5.5 0.23 2.55E+01 0.15Example 31 Presence −0.55 2.96E+05 6.66E−03 6.35E+12 5.2 0.22 5.68E+030.14 Example 32 Presence −0.79 5.96E+05 6.86E−03 5.64E+12 5.4 0.209.00E+03 0.17 Example 33 Presence −0.72 7.56E+06 2.50E−03 2.22E+15 0.530.52 2.55E+01 0.13 Example 34 Presence −0.75 8.99E+06 2.20E−03 3.55E+150.57 0.21 2.22E+01 0.60 Example 35 Presence −0.79 9.22E+05 3.66E−033.56E+15 0.45 0.35 4.55E+01 0.15 Example 36 Presence −0.47 1.39E+061.50E+02 2.46E+16 0.23 0.23 2.88E+01 0.13 Example 37 Presence −0.481.75E+06 1.00E+01 1.62E+16 0.22 0.23 6.40E+01 0.13 Example 38 Presence−0.58 1.56E+06 2.00E+02 3.12E+16 0.25 0.23 8.40E+01 0.11 Evaluation ofcharacteristics of matrix domain configuration Domain Electronicelectro- conductive material Image evaluation Equivalent Particle cross-Black and circle size sectional Perimeter Shape Domain white diameterdistribution area ratio index volume potential Ghost D σd/D ratio μr A/BNumber fraction difference image μm — % — % % V — Example 22 4.4  0.2526.6 1.10 86 23.8 36 B Example 23 4.6  0.24 20.6 1.04 89 24.1 40 CExample 24 5.7  0.23 26.5 1.09 86 23.2 45 C Example 25 0.23 0.22 26.21.05 90 14.3 25 B Example 26 1.34 0.21 26.4 1.05 90 13.9 26 B Example 271.11 0.20 20.7 1.02 83 13.5 27 B Example 28 0.22 0.22 20.5 1.01 87 13.228 B Example 29 4.93 0.22 26.3 1.08 95 22.6 40 C Example 30 4.85 0.2226.3 1.05 91 23.8 48 C Example 31 4.36 0.21 21.8 1.04 82 23.2 42 CExample 32 4.42 0.23 21.0 1.08 92 23.8 48 C Example 33 2.3  0.55 26.91.06 88 23.4 41 C Example 34 1.57 0.23 26.9 1.06 85 23.0 42 C Example 351.23 0.31 20.6 1.20 56 23.7 45 C Example 36 1.15 0.23 26.6 1.04 94 14.135 B Example 37 1.26 0.21 26.2 1.03 87 13.9 31 B Example 38 1.33 0.2126.8 1.06 81 13.8 40 C

Example 39

An electroconductive roller B1 was manufactured in the same manner as inExample 1 except that the diameter of the electroconductive support waschanged to 5 mm and the outer diameter of the electroconductive memberafter polishing was 10.0 mm.

The electroconductive roller B1 was used as a transfer member for thefollowing evaluations.

As an electrophotographic apparatus, an electrophotographic laserprinter (product name: Laserjet M608dn, available from HP) was prepared.

First, the electroconductive roller B1 and the laser printer were leftin an environment of 23° C. and 50% for 48 hours for the purpose ofadjusting to the measurement environment.

Next, the electroconductive roller B1 was incorporated into the laserprinter as a transfer member. In order to evaluate in a high-speedprocess, the laser printer was modified so that the number of outputsheets per unit time was 75 sheets/minute with A4 size paper, which waslarger than the number of original output sheets. At that time, theoutput speed of the recording medium was 370 mm/sec and the imageresolution was 1,200 dpi. Also, it was left in an environment of 23° C.and 50% for 48 hours.

The electrophotographic apparatus was modified so as to measure thesurface potential of the back surface, of the recording medium A4 sizepaper, opposite to the surface on which the developer was transferred. Asurface electrometer and a probe for measuring the surface potentialused were the same as those used in the examples of the charging roller.

As a result of evaluating the difference in the surface potentialbetween the portion with the developer and the back surface, of the A4size paper without the developer, which is opposite to the surface onwhich the developer is transferred, the difference was 5 V.

COMPARATIVE EXAMPLE Comparative Example 1

An electroconductive member C1 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used. Then, according to the following method, anelectroconductive resin layer was further provided on theelectroconductive support C1 to manufacture an electroconductive rollerC1, and the same measurement and evaluation as in Example 1 wereperformed. The results are indicated in Table 9.

First, methyl isobutyl ketone as a solvent was added to acaprolactone-modified acrylic polyol solution to adjust the solidcontent to 10% by mass. With respect to 1,000 parts by mass of thisacrylic polyol solution (100 parts by mass of solid content), a mixedsolution was prepared using the materials indicated in Table 7 below. Atthis time, the mixture of block HDI and block IPDI had “NCO/OH=1.0”.

TABLE 7 Blending amount (Parts by Raw material name mass) Main agentCaprolactone modified acrylic polyol 100 solution (Solid content: 70% bymass) (Solid (Product name: PLACCEL DC2016, content) available fromDaicel Corporation) Curing agent 1 Blocked isocyanate A 37 (IPDI, Solidcontent: 60% by mass) (Solid (Product name: VESTANAT B1370, content)available from Evonik) Curing agent 2 Blocked isocyanate B (HDI, Solid24 content 80% by mass) (Solid (Product name: DURANATE content)TPA-B80E, available from Asahi Kasei Chemicals Corporation)Electroconductive Carbon black (HAF) 15 agent (Product name: Seast3,available from Tokai Carbon Co., Ltd.) Additive 1 Needle-shaped rutiletitanium 35 oxide fine particles (Product name: MT-100T, available fromTeika) Additive 2 Modified dimethyl silicone oil 0.1 (Product name:SH28PA, available from Toray Dow Corning Silicone)

Then, 210 g of the above mixed solution, 200 g of glass beads having anaverage particle diameter of 0.8 mm as a medium were mixed in a 450 mLglass bottle, and predispersed for 24 hours using a paint shakerdisperser, thereby obtaining a paint for forming an electroconductiveresin layer.

The electroconductive support C011 was dipped into the paint for formingthe electroconductive resin layer with the longitudinal direction beingthe vertical direction, and applied by a dipping method. The dippingtime for dip-coating was nine seconds, the initial pull-up speed was 20mm/sec, the final pull-up speed was 2 mm/sec, and during that time, thespeed was changed linearly with time. The obtained coated product wasair-dried at room temperature for 30 minutes, then dried for one hour ina hot air circulation dryer set at 90° C., and further dried for onehour in the hot air circulation dryer set at 160° C. so as to obtain anelectroconductive roller C1. The evaluation results are indicated inTable 9.

In this comparative example, the electroconductive layer has only asingle layer made of an electroconductive material, and thus has asingle electroconductive path as an electroconductive member. Therefore,the slope of the impedance was −1 in the high frequency region, and theghost image was rank D.

Comparative Example 2

An electroconductive member C2 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, the electroconductive layer has only asingle layer made of an electroconductive material, and thus has asingle electroconductive path as an electroconductive member. Therefore,the slope of the impedance was −1 in the high frequency region, and theghost image was rank D.

Comparative Example 3

An electroconductive member C3 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed.

The results are indicated in Table 9.

In this comparative example, although the domains and the matrix areincluded, the matrix is an ionic electroconductive base layer, so thatthe matrix eventually has a single electroconductive path as anelectroconductive member. Therefore, the slope of the impedance was −1in the high frequency region, and the ghost image was rank D.

Comparative Example 4

An electroconductive member C4 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, the volume resistivity of the matrix islow, and the electroconductive member has a single electroconductivepath. Therefore, the slope of the impedance was −1 in the high frequencyregion, and the ghost image was rank D.

Comparative Example 5

An electroconductive member C5 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, although the matrix-domain structure isused, the volume resistivity of the matrix is low, the movement ofelectric charges cannot be limited to the domains, the state of leakingto the matrix is reduced, and the easiness of discharge is reduced.Therefore, the impedance in the low frequency region increased and theghost image was rank D.

Comparative Example 6

An electroconductive member C6 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, although the matrix-domain structure isused, the volume resistivity of the domain is high and the resistance ofthe matrix is low, and the electroconductive member has a singlecontinuous electroconductive path. Therefore, the slope of the impedancewas −1 in the high frequency region, and the ghost image was rank D.

Comparative Example 7

An electroconductive member C7 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, the electroconductive phase and theinsulating phase have a bicontinuous structure instead of thematrix-domain structure. That is, the electroconductive member has asingle electroconductive path. Therefore, the slope of the impedance was−1 in the high frequency region, and the ghost image was rank D.

Comparative Example 8

An electroconductive member C8 was manufactured in the same manner as inExample 1 except that the materials and conditions indicated in Table8-1 and Table 8-2 were used, and the same measurements and evaluationsas in Example 1 were performed. The results are indicated in Table 9.

In this comparative example, as the electroconductive member, theimpedance value on the low frequency side was high, charging wasinsufficient, image output was not possible, and therefore, evaluationwas impossible.

TABLE 8-1 Unvulcanized domain rubber composition ElectroconductiveElectroconductive agent support Raw material rubber type PartsDispersion Electroconductive SP Mooney by time Mooney Type surfaceMaterial abbreviation value viscosity Type mass DBP min viscosityComparative SUS Ni plating NBR N230SV 19.2 32 LV 3 — 30 35 Example 1Comparative SUS Ni plating NBR N230SV 19.2 32 #7360 50 87 30 60 Example2 Comparative SUS Ni plating NBR N230SV 19.2 32 Ketjen 10 360 30 50Example 3 Comparative SUS Ni plating NBR N230SV 19.2 32 #7360 60 87 3065 Example 4 Comparative SUS Ni plating BR JSR T0700 17.1 43 #7360 80 8730 85 Example 5 Comparative SUS Ni plating SBR T2003 17 45 — — — — 45Example 6 Comparative SUS Ni plating BR JSR T0700 17.1 43 #7360 80 87 3085 Example 7 Comparative SUS Ni plating BR JSR T0700 17.1 43 #7360 80 8730 85 Example 8

TABLE 8-2 Unvulcanized Unvulcanized rubber rubber Unvulcanized matrixrubber composition composition dispersion Vulcanizing VulcanizationFiller Domain Matrix Rotat- Knead- agent accelerator Rubber typeMaterial Parts Parts Parts ion ing Material Parts Material Parts SPMooney abbrevi- by Mooney by by speed time abbrevi- by abbrevi- byMaterial abbreviation value viscosity ation mass viscosity mass mass rpmmin ation mass ation mass Comparative — — — — — — — 100  0 — — Sulfur 3TBZTD 1 Example 1 Comparative — — — — — — — 100  0 — — Sulfur 3 TBZTD 1Example 2 Comparative ECO CG103 18.5 64 LV  3 72 20 80 30 20 Sulfur 3TBZTD 1 Example 3 Comparative SBR T2003 17 55 #7360 20 60 25 75 30 20Sulfur 3 TBZTD 1 Example 4 Comparative NBR N2305V 19.2 32 — — 37 25 7530 20 Sulfur 3 TBZTD 1 Example 5 Comparative NBR N2305V 19.2 65 #7360 6074 75 25 30 20 Sulfur 3 TBZTD 1 Example 6 Comparative EPDM Esplene505A16 47 — — 53 60 40 30 20 Sulfur 3 TET 3 Example 7 Comparative EPDMEsplene505A 16 47 — — 56 10 90 30 20 Sulfur 3 TET 3 Example 8

Comparative Example 9

[Manufacture of Unvulcanized Rubber Mixture for Forming Domain (CMB)]

The materials indicated in Table 8-3 were mixed in the blending amountsindicated in Table 8-3. The mixing conditions were the same as for CMBin Example 1.

TABLE 8-3 Blending amount (Parts by Raw material name mass) Raw materialButadiene rubber 100 rubber (Product name: JSR T0700, available from JSRCorporation Mooney viscosity ML(1 + 4)100° C.: 43 SP value: 17.1(J/cm³)^(0.5)) Electronic Carbon black 85 electroconductive (Productname: TOKABLACK agent #7360, available from Tokai Carbon Co., Ltd.) DBPoil absorption: 87 cm³/100 g pH: 7.5) Vulcanization Zinc oxide 5accelerator (Product name: Zinc oxide, available from Sakai ChemicalIndustry Co., Ltd.) Processing aid Zinc stearate 2 (Product name:SZ-2000), available from Sakai Chemical Industry Co., Ltd.)

Each material indicated in Table 8-4 was added to 100 parts by mass ofthe CMB obtained above in the blending amount indicated in Table 8-4,and mixed under the same mixing conditions at the time of preparing therubber mixture for forming an electroconductive layer of Example 1 so asto prepare CMB.

TABLE 8-4 Blending amount (Parts by Raw material name mass) VulcanizingSulfur 3 agent (Product name: SULFAX PMC, available from TsurumiChemical Industry Co., Ltd.) Vulcanization Tetraethyl thiuram disulfide3 aid (Product name: NOCCELER TET-G, available from Ouchi ShinkoChemical Industrial Co., Ltd)

[Preparation of Rubber Particles for Domain Molding]

The obtained CMB was placed in a mold having a thickness of 2 mm andvulcanized by a hot press at a pressure of 10 MPa and a temperature of160° C. for 30 minutes. The rubber sheet was taken out from the mold andcooled to room temperature to obtain a vulcanized rubber sheet of therubber composition for molding a domain having a thickness of 2 mm.

The obtained vulcanized rubber sheet was dipped in liquid nitrogen for48 hours, completely frozen, and then crushed with a hammer to formcoarse powder. Thereafter, using a collision type supersonic jet crusher(product name: CPY+USF-TYPE, available from Nippon Pneumatic Mfg. Co.,Ltd.), freeze pulverization and classification were simultaneouslyperformed to obtain vulcanized rubber particles for forming a domain.

[Preparation of Rubber Mixture for Forming Matrix (MRC)]

Each material indicated in Table 8-5 was mixed in the blending amountindicated in Table 8-5, and mixed under the same mixing conditions as inthe preparation of MRC in Example 1 so as to obtain MRC.

TABLE 8-5 Blending amount (Parts by Raw material name mass) Raw materialEPDM (Product name: 100 rubber Esplene505A, available from SumitomoChemical Company, Limited Mooney viscosity ML(1 + 4)100° C.: 47 SPVALUE: 16.0 (J/cm³)^(0.5))) Filler Calcium carbonate 70 (Product name:NANOX #30, available from Marua Calcium Co., Ltd.) Vulcanization Zincoxide (Product name: 7 accelerator Zinc oxide, available from SakaiChemical Industry Co., Ltd.) Processing aid Zinc stearate (Product name:2.8 SZ-2000, available from Sakai Chemical Industry Co., Ltd.)

[Preparation of Rubber Mixture for Forming Electroconductive Layer]

The vulcanized rubber particles for forming a domain obtained above andMRC were mixed in the blending amount indicated in Table 8-6 so as toobtain an unvulcanized rubber mixture. A 6-liter pressure kneader(product name: TD6-15MDX, available from Toshin) was used as a mixer.The mixing conditions were a filling rate of 70 vol %, a blade rotationspeed of 30 rpm, and 16 minutes of time duration.

TABLE 8-6 Raw material for unvulcanized rubber composition Blendingamount (Parts by Raw material name mass) Raw material Rubber particlefor domain molding 25 rubber Raw material MRC 75 rubber

Each material indicated in Table 8-7 was added to 100 parts by mass ofthe unvulcanized rubber mixture obtained above in the blending amountindicated in Table 8-7, and mixed under the same mixing methods at thetime of preparing the rubber mixture for forming an electroconductivelayer of Example 1 so as to prepare a rubber mixture for forming anelectroconductive layer.

TABLE 8-7 Raw material of rubber composition for formingelectroconductive member Blending amount (Parts Raw material name bymass) Vulcanizing Sulfur 3 agent (Product name: SULFAX PMC, availablefrom Tsurumi Chemical Industry Co., Ltd.) Vulcanization Tetraethylthiuram disulfide 3 aid (Product name: NOCCELER TET-G, available fromOuchi Shinko Chemical Industrial Co., Ltd)

An electroconductive roller C9 was manufactured in the same manner as inExample 1 except that the rubber mixture for forming anelectroconductive layer was used, and the same measurements andevaluations as in Example 1 were performed. The results are indicated inTable 9.

In this comparative example, since the anisotropic electroconductiverubber particles formed by freeze pulverization, which are large insize, are dispersed, the electroconductive paths in theelectroconductive member are unevenly formed, which is synonymous withthe state where the thickness of the domain is large. As a result, theslope of the impedance was −1 at a high frequency, and the ghost imagewas rank D.

Comparative Example 10

[Preparation of Unvulcanized Hydrin Rubber Composition]

Each material as indicated in Table 8-8 was kneaded under the sameconditions as in the preparation of the unvulcanized domain rubbercomposition of Example 1 so as to prepare an unvulcanized hydrin rubbercomposition.

TABLE 8-8 Raw material for unvulcanized hydrin rubber compositionBlending amount (Parts by Raw material name mass) Raw materialEpichlorohydrin rubber (EO-EP-AGE 100 rubber ternary co-compound)(Product name: EPICHLOMER CG103, available from Osaka Soda Co., Ltd. SPvalue: 18.5 (J/cm³)^(0.5)) Ionic LV-70 3 electroconductive (Productname: ADK CIZER LV70, agent available from ADEKA) Plasticizer Aliphaticpolyester plasticizer 10 (Product name: POLYCIZER P-202, available fromDIC) Filler Calcium carbonate 60 (Product name: NANOX #30, availablefrom Maruo Calcium Co., Ltd.) Vulcanization Zinc oxide 5 accelerator(Product name: Zinc oxide, available from Sakai Chemical Industry Co.,Ltd.) Processing aid Zinc stearate 1 (Product name: SZ-2000), availablefrom Sakai Chemical Industry Co., Ltd.)

Then, each material as indicated in Table 8-9 was kneaded under the sameconditions as in the preparation of the rubber composition for formingan electroconductive member of Example 1 so as to prepare a hydrinrubber composition for a first electroconductive elastic layer.

TABLE 8-9 Hydrin rubber composition for forming electroconductive memberBlending amount (Parts by Raw material name mass) Raw materialUnvulcanized hydrin rubber 100 rubber composition Vulcanizing Sulfur 1.8agent (Product name: SULFAX PMC, available from Tsurumi ChemicalIndustry Co., Ltd.) Vulcanization Tetramethyl thiuram monosulfide 1 aid1 (Product name: NOCCELER TS, available from Ouchi Shinko ChemicalIndustrial Co., Ltd) Vulcanization 2-Mercaptobenzimidazole 1 aid 2(Product name: NOCRAC MB, available from Ouchi Shinko ChemicalIndustrial Co., Ltd)

Next, the rubber composition for molding an electroconductive member ofExample 1 was prepared for a second electroconductive elastic layer.

In order to mold the prepared hydrin rubber composition and the rubbercomposition for forming an electroconductive member around anelectroconductive shaft core, two-layer extrusion was performed using atwo-layer extrusion device as illustrated in FIG. 16. FIG. 16 is aschematic diagram of a two-layer extrusion step. An extruder 162includes a two-layer crosshead 163. With the two-layer crosshead 163, itis possible to manufacture the electroconductive member 166 in which thesecond electroconductive elastic layer is laminated on the firstelectroconductive elastic layer using two types of unvulcanized rubbers.an electroconductive shaft core 161 sent by a core feeding roller 164rotating in the direction of the arrow is inserted into the two-layercrosshead 163 from behind. An unvulcanized rubber roller 165 whoseperiphery is covered with two types of unvulcanized rubber layers isobtained by integrally extruding two types of cylindrical unvulcanizedrubber layers simultaneously with the electroconductive shaft core 161.The unvulcanized rubber roller 165 thus obtained is vulcanized using ahot air circulating furnace or an infrared drying furnace. Then, thevulcanized rubber at both ends of the electroconductive layer is removedto obtain the electroconductive member 166.

The temperature of the two-layer crosshead was adjusted to 100 degreesand the outer diameter of an extrudate after extrusion was adjusted to 9mm. Next, an electroconductive shaft core was prepared and extrudedtogether with the raw material rubber to simultaneously form twocylindrical raw material rubber layers around the core metal to obtainan unvulcanized rubber roller. Then, the unvulcanized rubber roller wasput into a hot air vulcanizing furnace at 160° C. and heated for onehour, and two-layer elastic roller having a hydrin base layer (firstelectroconductive elastic layer) on the outer peripheral portion of thesupport and a surface layer (second electroconductive elastic layer)having a matrix-domain structure on the outer peripheral portion thereofwas obtained. The thickness ratio of the base layer and the surfacelayer and the overall outer diameter were adjusted during extrusion sothat the thickness of the surface layer was 1.0 mm. After that, bothends of the electroconductive layer were cut off by 10 mm to set alength of an electroconductive layer portion in the longitudinaldirection to be 231 mm.

Finally, the surface of the electroconductive layer was polished with arotary grindstone. As a result, an electroconductive member C10 wasmanufactured as an electroconductive roller having a crown shape with adiameter of 8.4 mm at a position of 90 mm from the central portion toboth end sides and a central portion diameter of 8.5 mm, and the samemeasurements and evaluations as in Example 1 were performed. The resultsare indicated in Table 9. In this comparative example, a thin layerhaving a matrix-domain structure is formed on the outer periphery of anionic electroconductive base layer having a medium resistance.Therefore, since the slope of the impedance is governed by thecharacteristics of the ionic electroconductive base layer in the highfrequency region, the slope of the impedance was −1 at a high frequency,and the ghost image was rank D.

TABLE 9 Evaluation of characteristics of matrix domain configurationMatrix Uniformity Impedance characteristics of inter- DomainElectroconductive Inter- domain Volume Presence layer Electroconductivedomain surface resistivity of sea- (a) (b) support Volume surfacedistances Volume uniformity island Slope Impedance Impedance resistivitydistances σm/Dm resistivity σr/μr structure a.u. Ω Ω Ωcm μm — Ωcm —Comparative Absence −1 2.56E+08 8.79E−03 — — — — — Example 1 ComparativeAbsence −1 6.22E+07 9.51E−03 — — — — — Example 2 Comparative Presence −15.12E+08 5.60E−03  1.44E+07 0.56 0.32 1.25E+01 0.15 Example 3Comparative Presence −1 6.15E+06 5.20E−03  1.87E+07 0.21 0.25 2.55E+010.14 Example 4 Comparative Presence −1 1.57E+07 6.33E−03  2.58E+09 0.230.26 5.21E+01 0.16 Example 5 Comparative Presence −1 2.21E+04 9.23E−03 9.18E+02 2.2 0.22 2.56E+15 — Example 6 Comparative Absence −1 1.60.E+055.50E−03 — — — — — Example 7 Comparative Presence −0.29 3.21E+091.56E−03  6.56E+15 0.23 0.33 2.89E+01 0.14 Example 8 ComparativePresence −0.97 6.97.E+04 4.20.E−03 9.271E+15 18 0.55 8.3.E+01 0.22Example 9 Comparative Presence −1 1.50.E+06 2.50E+06  8.70E+15 0.21 0.256.22E+01 0.15 Example 10 Evaluation of characteristics of matrix domainconfiguration Domain Electronic Image evaluation Equivalentelectroconductive Black and circle material cross- Perimeter Domainwhite diameter sectional area ratio Shape volume potential Ghost D ratioμr A/B index fraction difference image μm % — Number % % V — Comparative— — — — — 60 D Example 1 Comparative — — — — — 62 D Example 2Comparative 1.20 15.2 1.02 55 19.7 65 D Example 3 Comparative 2.20 25.11.05 84 24.6 66 D Example 4 Comparative 2.30 26.3 1.02 86 24.3 62 DExample 5 Comparative 2.50 — 1.02 85 75.6 60 D Example 6 Comparative — —— — — 60 D Example 7 Comparative 0.25 26.3 1.03 87 10.5 — D Example 8Comparative 12 27.8 1.30 32 25.0 — D Example 9 Comparative 0.23 26.11.08 82 15.3 63 D Example 10

While the present disclosure has been described with reference toexemplary embodiments, it is to be understood that the disclosure is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An electrophotographic electroconductive membercomprising: a support having an electroconductive outer surface; and anelectroconductive layer on the electroconductive outer surface of thesupport, the electroconductive layer having a matrix comprising a firstrubber, and domains dispersed in the matrix, the domains each comprisinga second rubber and an electronic electroconductive agent, whereinassuming that a metal film is provided on the electroconductive outersurface of the electroconductive member, and impedance is measured byapplying an AC voltage with an amplitude of 1 V between theelectroconductive outer surface of the support and the metal film whilevarying a frequency between 1.0×10⁻² Hz to 1.0×10⁷ Hz under anenvironment of a temperature of 23° C. and a humidity of 50% RH, in adouble logarithmic plot with a frequency on an abscissa and an impedanceon an ordinate, a slope at frequencies of 1.0×10⁵ Hz to 1.0×10⁶ Hz is−0.8 or more and −0.3 or less, and an impedance at frequency of 1.0×10⁻²Hz to 1.0×10¹ Hz is 1.0×10³ to 1.0×10⁷Ω.
 2. The electroconductive memberaccording to claim 1, wherein the electroconductive layer is directlyprovided on the electroconductive outer surface of the support.
 3. Theelectroconductive member according to claim 1, further comprising anelectroconductive resin layer between the electroconductive layer andthe electroconductive outer surface of the support, assuming that ametal film is provided on an outer surface of the resin layer, andimpedance is measured by applying an AC voltage with an amplitude of 1 Vbetween the electroconductive outer surface of the support and the metalfilm while varying a frequency between 1.0×10⁻² Hz to 1.0×10⁷ Hz underan environment of a temperature of 23° C. and a humidity of 50% RH, in adouble logarithmic plot with a frequency on an abscissa and an impedanceon an ordinate, an impedance at 1.0×10⁻² Hz to 1.0×10¹ Hz is 1.0×10⁻⁵ to1.0×10²Ω.
 4. The electroconductive member according to claim 1, whereinvolume resistivity of the matrix is more than 1.0×10¹² Ω·cm and 1.0×10¹⁷Ω·cm or less.
 5. The electroconductive member according to claim 1,wherein an arithmetic average value Dm of a distance between the domainsis 0.2 μm or more and 2.0 μm or less.
 6. The electroconductive memberaccording to claim 1, wherein the support is a cylindrical support, andthe electroconductive layer is provided on an outer peripheral surfaceof the cylindrical support.
 7. The electrophotographic electroconductivemember according to claim 6, wherein defining a length of thecylindrical support of the electroconductive layer in the longitudinaldirection as L, and defining a thickness of the electroconductive layeras T, and assuming that three cross sections of the electroconductivelayer in a thickness direction thereof at a center in the longitudinaldirection of the electroconductive layer, and L/4 from both ends of theelectroconductive layer toward the center, are obtained, where Lrepresents a length of the electroconductive layer in the longitudinaldirection of the cylindrical support, and assuming that at each of thecross sections, three square observation areas each having 15 μm a side,are arbitrary placed in a thickness region from 0.1T to 0.9T in depthfrom the outer surface of the electroconductive layer, where Trepresents a thickness of the electroconductive layer, among domainsobserved in each of the nine observation areas, 80% by number or more ofthe domains satisfy the following requirements (1) and (2): (1) a ratioof a cross-sectional area of a part containing the electronicelectroconductive agent contained in the domain to a cross-sectionalarea of the domain is 20% or more; and (2) when defining a perimeter ofthe domain as A, and defining an envelope perimeter of the domain as B,A/B is 1.00 or more and 1.10 or less.
 8. The electroconductive memberaccording to claim 1, wherein when defining the arithmetic average valueof an equivalent circle diameter of the domain as D and a standarddeviation of distribution of the D as σd, a variation coefficient σd/Dof the equivalent circle diameter of the domain is 0 or more and 0.4 orless.
 9. The electroconductive member according to claim 1, wherein whendefining the arithmetic average value of the inter-domain surfacedistances as Dm and the standard deviation of distribution of Dm as σm,the variation coefficient σm/Dm of the inter-domain surface distances is0 or more and 0.4 or less.
 10. The electroconductive member according toclaim 1, wherein when a mean value of ratios of cross-sectional areas ofmoieties of the electroconductive agent contained in each of the domainsappearing in a cross section in the thickness direction of theelectroconductive layer to each of cross-sectional areas of therespective domains is defined as μr, a standard deviation of the ratiosis defined as σr, a coefficient of variation σr/μr of the ratios of thecross-sectional areas of the moieties of the electroconductive agent is0 or more and 0.4 or less.
 11. The electroconductive member according toclaim 1, wherein the electroconductive member is a charging member. 12.The electroconductive member according to claim 1, wherein theelectroconductive member is a transfer member.
 13. A process cartridgeconfigured to be detachably attachable to a main body of anelectrophotographic image forming apparatus, the process cartridge forelectrophotography comprising an electroconductive member, theelectrophotographic electroconductive member including: a support havingan electroconductive outer surface; and an electroconductive layer onthe electroconductive outer surface of the support, theelectroconductive layer having a matrix comprising a first rubber, anddomains dispersed in the matrix, the domains each comprising a secondrubber and an electronic electroconductive agent, wherein assuming thata metal film is provided on the electroconductive outer surface of theelectroconductive member, and impedance is measured by applying an ACvoltage with an amplitude of 1 V between the electroconductive outersurface of the support and the metal film while varying a frequencybetween 1.0×10⁻² Hz to 1.0×10⁷ Hz under an environment of a temperatureof 23° C. and a humidity of 50% RH, in a double logarithmic plot with afrequency on an abscissa and an impedance on an ordinate, a slope atfrequencies of 1.0×10⁵ Hz to 1.0×10⁶ Hz is −0.8 or more and −0.3 orless, and an impedance at frequency of 1.0×10⁻² Hz to 1.0×10¹ Hz is1.0×10³ to 1.0×10⁷Ω.
 14. An electrophotographic image forming apparatuscomprising an electroconductive member, the electrophotographicelectroconductive member including: a support having anelectroconductive outer surface; and an electroconductive layer on theelectroconductive outer surface of the support, the electroconductivelayer having a matrix comprising a first rubber, and domains dispersedin the matrix, the domains each comprising a second rubber and anelectronic electroconductive agent, wherein assuming that a metal filmis provided on the electroconductive outer surface of theelectroconductive member, and impedance is measured by applying an ACvoltage with an amplitude of 1 V between the electroconductive outersurface of the support and the metal film while varying a frequencybetween 1.0×10⁻² Hz to 1.0×10⁷ Hz under an environment of a temperatureof 23° C. and a humidity of 50% RH, in a double logarithmic plot with afrequency on an abscissa and an impedance on an ordinate, a slope atfrequencies of 1.0×10⁵ Hz to 1.0×10⁶ Hz is −0.8 or more and −0.3 orless, and an impedance at frequency of 1.0×10⁻² Hz to 1.0×10¹ Hz is1.0×10³ to 1.0×10⁷Ω.